Permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film and a process for obtaining same

ABSTRACT

A permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film; a layer configuration comprising the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film exclusive of foam; a non-transparent microvoided thermally transparentizable axially stretched self-supporting polymeric film; and a process for obtaining a permanent transparent pattern comprising the step of: image-wise application of heat optionally supplemented by the application of pressure to the non-transparent microvoided axially stretched self-supporting polymeric film.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/850,512 filed Oct. 10, 2006, U.S. Provisional Application No. 60/850,511 filed Oct. 10, 2006, U.S. Provisional Application No. 60/908,526 filed Mar. 28, 2007, U.S. Provisional Application No. 60/908,536 filed Mar. 28, 2007, U.S. Provisional Application No. 60/908,542 filed Mar. 28, 2007, U.S. Provisional Application No. 60/908,545 filed Mar. 28, 2007, all incorporated by reference. In addition, this application claims the benefit of European Application No. 06121669.3 filed Oct. 3, 2006, European Application No. 06121665.1 filed Oct. 3, 2006, European Application No. 07104953.0 filed Mar. 27, 2007, European Application No. 07104947.2 filed Mar. 27, 2007, European Application No. 07104948.0 filed Mar. 27, 2007, and European Application No. 07104950.6 filed Mar. 27, 2007, which are all also incorporated by reference.

FIELD OF THE INVENTION

The present invention concerns permanent transparent patterns in non-transparent microvoided films, applications thereof, and a process for obtaining a permanent transparent pattern in non-transparent microvoided films.

BACKGROUND OF THE INVENTION

Permanent transparent patterns, examples of which are so-called watermarks and so-called pseudo-watermarks, are desirable for documents for anti-falsification, security and traceability applications e.g. banknotes, share certificates, tickets, credit cards, identity documents and labels for luggage and packages. Permanent transparent patterns in a paper support, such as so-called watermarks, can be realized during the manufacturing process.

EP-A 0 203 499 discloses a method of applying a “pseudo watermark to paper, which method comprises the steps of preparing a sheet or roll of paper containing a suitable amount of a thermally sensitive material, and subsequently applying heat to a part of the surface of the paper in a manner to cause a region of the paper to become semi-translucent.

GB 1489084A discloses a method of producing a simulated watermark in a paper sheet, wherein the sheet is impregnated in the desired watermark pattern by a transparentizing composition which is itself fluent, and which is polymerizable upon being activated by radiation to yield an insoluble resin matrix having a refractive index approximating to that of the paper, and the composition is cured in situ by irradiating the sheet with activating radiation.

U.S. Pat. No. 3,453,358 discloses in a method of forming clear images in opaque pressure coalescible films which includes the steps of forming an image in such film, and stabilizing the image by fixing a densifying agent in the pores of the film, the improvement in that method which comprises subjecting the densified and stabilized film to a post-treatment which substantially completely collapses and destroys the porous nature of the coalescible coating on the film to permanently encapsulate the densifying agent and to render more transparent those areas of the film in which less than a maximum amount of densifying agent has been deposited.

EP 0 436 178A2 discloses a polymeric shaped article characterized in that said article is comprised of a continuous oriented polymer matrix having dispersed therein microbeads of a cross-linked polymer which are at least partially bordered by void space, said microbeads being present in an amount of 5-50% by weight based on the weight of said oriented polymer, said void space occupying 2-60% by volume of said article. EP 0 436 178A2 further discloses that said cross-linked polymer preferably comprises polymerizable organic material which is a member selected from the group consisting of an alkenyl aromatic compound having the general formula Ar—C(—R)═CH₂ wherein Ar represents an aromatic hydrocarbon radical, or an aromatic halohydracarbon radical of the benzene series and R is hydrogen or the methyl radical; acrylate-type monomers including monomers of the formula CH₂═C(—R′)—C(—OR)═O wherein R is selected from the group consisting of hydrogen and an alkyl radical containing from about 1 to 12 carbon atoms and R′ is selected from the group consisting of hydrogen and methyl; copolymers of vinyl chloride and vinylidene chloride, acrylonitrile and vinyl chloride, vinyl bromide, vinyl esters having the formula CH₂═CH—O—C(—R)═O wherein R is an alkyl radical containing from 2 to 18 carbon atoms; acrylic acid, methacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, oleic acid, vinylbenzoic acid; the synthetic polyester resins which are prepared by reacting terephthalic acid and dialkyl terephthalics or ester-forming derivatives thereof, with a glycol of the series HO(CH₂) OH, wherein n is a whole number within the range of 2-10 and having reactive olefinic linkages within the polymer molecule, the hereinabove described polyesters which include copolymerized therein up to 20 percent by weight of a second acid or ester thereof having reactive olefinic unsaturation and mixtures thereof, and a cross-linking agent selected from the group consisting of divinylbenzene, diethylene glycol dimethacrylate, diallyl fumarate, diallyl phthalate and mixtures thereof.

U.S. Pat. No. 5,660,925 discloses an authenticatible, tamper-indicating label, comprising: a normally opaque, transparentizable microporous film having first and second major surfaces, a first indicia proximate said first surface a second indicia on said first surface, and an adhesive proximate said first surface; wherein said microporous film can be changed from an opaque state to a transparent state by application of a first liquid that is not a solvent for said first and second indicia to said microporous film to thereby sufficiently fill the pores of said microporous film to cause said film to become transparent; wherein when said microporous film is in its opaque state, said first and second indicia are not visually perceptible when said label is viewed from said second surface, and when said microporous film is in its transparent state, at least said first indicia is visually perceptible when said label is viewed from said second surface, thereby providing an indication of the authenticity of said label; and wherein application of a second liquid that is a solvent for said second indicia causes at least a portion of said second indicia to migrate through said microporous film to said second major surface, thereby providing a permanent visually perceptible indication of tampering. Us 5,660,925 discloses the realization of temporary transparency not permanent transparency.

U.S. Pat. No. 5,928,471 discloses a method of making a continuous roll of banknote paper on a paper making machine, said banknote paper having a low porosity and having a plurality of discrete transparentized regions repeating along the length of the paper, and also having a plurality of discrete areas repeating along the length of the paper which are at least partly of a lower grammage than surrounding areas, so as to provide lighter and darker areas in said areas which are enhanced by said transparentized regions, said method comprising the steps of: (a) continuously depositing an aqueous fibrous suspension onto a support surface to form continuous wet paper sheet; (b) forming in the wet paper sheet a series of discrete areas repeating along the length of the sheet which are at least partly of a lower grammage than surrounding areas; (c) draining liquid from said wet paper sheet to form a continuous unfinished porous absorbent sheet; (d) printing a plurality of locations in said unfinished porous sheet with a transparentized resin to provide transparentized regions which cooperate with the discrete lower grammage areas to enhance the visibility thereof, which transparentising resin is absorbed into the sheet; (e) passing said unfinished porous sheet having the discrete printed transparentized regions through a surface sizing impregnating device so as to impregnate said porous sheet with surface sizing, such that the surface sizing surrounds the transparentized regions; (f) drying the resulting sized porous sheet to form a dried porous sheet; (g) calendering said dried porous sheet; and (h) reeling the resulting sheet into a roll of finished banknote paper.

US 2005/0116463A1 discloses a process for producing a security feature, in particular on print media, in particular passes and identity cards, plastic payment cards, credit cards, memory cards etc, wherein the substrate (1, 1a, 1b) includes at least one change-over substance which by virtue of irradiation with light of a given wavelength (λ, λ1, λ2) experiences an irreversible change in color from a starting color to a final color, characterized in that the substrate when in the initial condition is so irradiated by a controlled light beam of that wavelength (λ, λ1, λ2), in particular a laser beam, that due to the change in color caused thereby in the change-over substance an image which can be recognized especially with the naked eye is produced on the substrate (1).

US 2005/0104365A1 discloses a security substrate comprising at least one oriented, high melt-strength polypropylene foam layer and at least one security element with a preferred security element being an embossment which provides a substantially transparent region with substantially transparent meaning at least about 20 percent, preferably at least 30 percent, of 400 to 700 nm wavelength light passing through a 1-mm thick region. US 2005/0104365A1 fails to define the term “foam”. Therefore, the term “foam” as used in disclosing the invention of US 2005/0104365A1 has the meaning in plain English i.e. is a substance that is formed by trapping many gas bubbles in a liquid or solid. US 2005/0104365A1 discloses in comparative examples that microvoided materials gave very poor transparency upon embossment.

WO 2004/043708A discloses a laminated security document comprising: a transparent or translucent support layer; a first security layer provided on one side of the support layer; a second security layer provided on the opposite side of the support layer; the first and second security layers having security regions which together form a composite security image or device to indicate an authentic security state; a first tamper evident means provided between the support layer and the first security layer; a second tamper evident means provided between the support layer and the second security layer; wherein upon exposure of the security document to predetermined conditions to laminate the document, at least one of the tamper evident means is arranged to destruct or otherwise affect at least one of the security layers to indicate an unauthentic security state.

U.S. Pat. No. 4,526,803 discloses a method for electrostatically transparentizing a portion of a substrate, comprising: selecting finely divided, electrostatically chargeable particles of a material having transparentizing characteristics for a preselected substrate; electrostatically depositing said finely divided transparentizing particles onto a predetermined area of the substrate; heating the transparentizing particles to form a molten transparentizing material at the predetermined area; and transparentizing the substrate at the predetermined area by flowing the molten transparentizing material into the substrate at the predetermined area and allowing the material to solidify therein to form a substrate having a transparentized area and an opaque area.

EP-A 0 618 079 discloses a thermal dye transfer system comprising a thermal dye transfer receptor element in intimate contact with a thermal dye donor sheet, said receptor element comprising a substrate having on at least one surface thereof in contact with said dye transfer donor sheet, an opaque dye receptive receiving layer comprising a thermally transparentizable microporous polymer layer having insufficient pigment to provide an optical density of more than 0.2.

JP 2005-271321A1 discloses the giving of a matt finish to the surface of a recording paper by using a thermal head by heating the protective layer to form a transparent watermark pattern as a result of the different glossiness in accordance with thermal energy given.

However, in all of these disclosures, except for paper, the transparentization has been realized in layers laminated to or applied to the support. Therefore, the prior art fails to teach the realization of a permanent transparent pattern in a polymer self-supporting film itself or a means of obtaining a permanent transparent pattern in a self-supporting polymer film.

Aspects of the Invention:

It is therefore an aspect of the present invention to provide a permanent transparent pattern in a self-supporting film.

It is therefore a further aspect of the present invention to provide a process for producing a permanent transparent pattern in a self-supporting film.

Further aspects and advantages of the invention will become apparent from the description hereinafter.

SUMMARY OF THE INVENTION

It has been surprisingly found that a permanent transparent pattern can be obtained by image-wise application of heat to an axially stretched non-transparent film comprising as a continuous phase polypropylene having dispersed therein calcium carbonate; a linear polyester matrix having uniformly dispersed therein a high polymer having a higher glass transition point than that of the linear polyester; a linear polyester matrix having uniformly dispersed therein a crystalline polymer having a higher melting point than that of the linear polyester; and a linear polyester having uniformly dispersed therein a pigment causing microvoiding.

Aspects of the present invention are realized by a permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film exclusive of foam.

Aspects of the present invention are also realized by the use of the above-described non-transparent microvoided axially stretched self-supporting polymeric film with a permanent transparent pattern as a synthetic paper.

Aspects of the present invention are also realized by a layer configuration comprising the above-described non-transparent microvoided film with a permanent transparent pattern.

Aspects of the present invention are also realized by a security document comprising the above-described non-transparent microvoided polymeric film with a transparent pattern.

Aspects of the present invention are also realized by a process for obtaining a permanent transparent pattern comprising the step of: image-wise application of heat optionally supplemented by the application of pressure to a non-transparent microvoided axially stretched self-supporting polymeric film exclusive of foam.

Preferred embodiments of the present invention are disclosed in the detailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION Definitions

The term voids or microvoids, as used in disclosing the present invention, means microcells, minute closed cells, cavities or pores or cellulation, which, for example, can be formed in an oriented polymeric film during stretching as the result of a void-initiating particle initiated by particles that are immiscible with the polymer matrix. The voids or microvoids can be unfilled or filled with air or a vapour of some sort. Even if initially unfilled the voids or microvoids may over time become filled with air or a vapour of some sort.

The term “opaque”, means a percentage opacity to visible light of greater than 90% as determined according to ASTM D589-97 or according to opacity test T425m-60 as published by TAPPI, 360 Lexington Avenue, New York, USA. Alternative measures of opacity are optical density and the transmittance of visible light. For example YUPO synthetic paper, see EXAMPLE 83, would generally be regarded as opaque and has an optical density of 1.25 as measured with a MacBeth TR924 densitometer with a visible filter. Measurements performed on “opaque PETG” foils from FOLIENWERK WOLFEN GMBH containing ca. 6% by weight of titanium dioxide with thicknesses of 500 μm and 50 μm were determined with an ULTRASCAN spectrophotometer to have transmittances of 0.3% and 21.5% respectively corresponding to optical densities of 2.52 and 0.67. Therefore foils with an optical density greater than 0.65 may be regarded as substantially opaque.

The term film, as used in disclosing the present invention, is an extruded sheet of a particular composition or a sheet consisting of a multiplicity of films with the same or different compositions produced by co-extrusion of liquids with the same or different compositions in contact with one another. The term film is also applied to axially and biaxially stretched films. The terms film and foil are used interchangeably in the present disclosure.

The term foam, as used in disclosing the present invention, means a substance that is formed by trapping many gas bubbles in a liquid or solid such as resulting from the incorporation of a chemical or physical blowing agent as disclosed in US 2005/0104365A1, WO 02/00982A1 and U.S. Pat. No. 6,468,451.

The term dicarboxylate monomer unit in a linear polyester, as used in disclosing the present invention, means a monomer unit derived either from a dicarboxylic acid or an ester thereof.

The term dimethylene aliphatic monomer unit in a linear polyester, as used in disclosing the present invention, means a monomer unit derived from a dimethylene aliphatic diol or an ether thereof, wherein the term aliphatic includes alicylic.

The term linear polyester, as used in disclosing the present invention, means a polyester comprising hydrocarbon dimethylene and dicarboxylate monomer units.

The term linear aromatic polyester, as used in disclosing the present invention, means a polyester comprising aliphatic dimethylene and aromatic dicarboxylate monomer units.

The term density, as used in disclosing the present invention, means the weight of a 100 mm×100 mm piece of film with a thickness measured in contact with an inductive probe with ball tip 3 mm in diameter divided by its volume. This value assumes that the surfaces of the piece of film are flat and parallel to one another. This value corresponds to the apparent density values reported in EP-A 0 496 323 and WO 2005/105903A.

The term thermally transparentizable, as used in disclosing the present invention, means capable upon the application of heat of providing an optical density difference of at least 0.2 as measured by a densitometer with a visible filter in the transmission mode e.g. using a MacBeth TR924 densitometer.

The term amorphous high polymer, as used in disclosing the present invention, means a polymer with a high molecular weight (sometimes arbitrarily designated as higher than 10,000) and a degree of crystallinity of less than 10%.

The degree of crystallinity can be determined by several experimental techniques including: (i) x-ray diffraction, with the degree of crystallinity=I_(c)/(I_(c)+K_(X)I_(a)), where I_(c), and I_(a) are the integrated intensities scattered over a suitable angular interval by the crystalline and the amorphous phases respectively and K_(X) is a calibration constant; (ii) calorimetry, with the degree of crystallinity=Δh_(fus)/Δh_(fus,c), where h_(fus) is the specific enthalpy of fusion of the sample and Δh_(fus,c) is the specific enthalpy of fusion of the completely crystalline polymer; (iii) density measurements, with the degree of crystallinity=ρ_(c)(ρ−ρ_(a))/[ρ(ρ_(c)−ρ_(a))], where ρ, ρ_(c) and ρ_(a) are the densities of the sample, of the completely crystalline polymer and of the completely amorphous polymer, respectively; and (iv) infra-red spectroscopy (IR), with the degree of crystallinity=(1/a_(c)ρ1)log₁₀(I₀/I), where I₀ and I are the incident and transmitted intensities respectively at the frequency of the absorption band due to the crystalline portion, a_(c) is the absorptivity of the crystalline material and 1 is the thickness of the sample.

The term crystalline high polymer, as used in disclosing the present invention, means a polymer with a high molecular weight (sometimes arbitrarily designated as higher than 10,000) with a degree of crystallinity of at least 10%.

The term inorganic opacifying pigment, as used in disclosing the present application, means a pigment capable of opacifying (i.e. rendering more opaque) which includes substantially white inorganic pigments having a refractive index of at least 1.4 and below 2.0 and pigments, which as a dispersion in a polymer are capable upon stetching of causing opacity due to microvoiding.

The term whitening agent, as used in disclosing the present invention, means a white/colourless organic compound which exhibits a blue luminescence under the influence of ambient UV-light.

The term “support”, as used in disclosing the present invention, means a “self-supporting material” so as to distinguish it from a “layer” which may be coated as a solution or dispersion, evaporated or sputtered on a support, but which itself is not self-supporting. It also includes an optional conductive surface layer and any treatment necessary for, or layer applied to aid, adhesion.

The term “watermark”, as used in disclosing the present invention, means a transparent image in a non-transparent background or a non-transparent image in a transparent background. A watermark may be detectable in transmission and/or reflection e.g. by holding the foil up to the light.

The term overprintable, as used in disclosing the present invention, means capable of being overprinted by conventional impact and/or non-impact printing processes.

The term conventional printing processes, as used in disclosing the present invention, includes but is not restricted to ink-jet printing, intaglio printing, screen printing, flexographic printing, offset printing, stamp printing, gravure printing, dye transfer printing, thermal sublimation printing and thermal and laser-induced processes.

The term pattern, as used in disclosing the present invention, means a non-continuous layer which can be in any form of lines, squares, circles or any random configuration.

The term layer, as used in disclosing the present invention, means a (continuous) coating covering the whole area of the entity referred to e.g. a support.

The term “non-transparent film”, as used in disclosing the present invention, means a film capable of providing sufficient contrast to a transparent image to make the image clearly perceptible. A non-transparent film can be an “opaque film”, but need not necessarily be completely opaque in that there is no residual translucence i.e. no light penetration through the film. Optical density in transmission as measured with a MacBeth TR924 densitometer through a visible filter can provide a measure of the non-transparency of a film. ISO 2471 concerns the opacity of paper backing and is applicable when that property of a paper is involved that governs the extent to which one sheet visually obscures printed matter on underlying sheets of similar paper and defines opacity as “the ratio, expressed as a percentage, of the luminous reflectance factor of a single sheet of the paper with a black backing to the intrinsic luminous reflectance factor of the same sample with a white reflecting backing. 80 g/m copy paper, for example, is white, non-transparent and has an optical density of 0.5 as measured with a MacBeth TR924 densitometer through a yellow filter according to ISO 5-2 and metallized films typically have an optical density ranging from 2.0 to 3.0.

The term transparent, as used in disclosing the present invention, means having the property of transmitting at least 50% of the incident visible light without substantially diffusing it and preferably at least 70% of the incident visible light without substantially diffusing it.

The term flexible, as used in disclosing the present invention, means capable of following the curvature of a curved object such as a drum e.g. without being damaged.

The term “colorant”, as used in disclosing the present invention, means dyes and pigments.

The term “dye”, as used in disclosing the present invention, means a colorant having a solubility of 10 mg/L or more in the medium in which it is applied and under the ambient conditions pertaining.

The term “pigment” is defined in DIN 55943, herein incorporated by reference, as an inorganic or organic, chromatic or achromatic colouring agent that is practically insoluble in the dispersion medium under the pertaining ambient conditions, hence having a solubility of less than 10 mg/L therein.

Permanent Transparent Pattern

Aspects of the present invention are realized by a permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film exclusive of foam.

According to a first embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film is a biaxially stretched film.

According to a second embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the pattern is visible in transmission i.e. with transmitted light in the wavelength range 400 to 700 nm.

According to a third embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the pattern is visible in reflection i.e. with reflected light in the wavelength range 400 to 700 nm.

According to a fourth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the pattern has an optical density difference in respect of the background of at least 0.15, preferably at least 0.25, particularly preferably at least 0.35 and especially preferably at least 0.45.

According to a fifth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the pattern has an optical density difference in respect of the background of at least 15%, preferably at least 25%, particularly preferably at least 35% and especially preferably at least 45%.

According to a sixth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, in a continuous phase linear polyester matrix is uniformly dispersed from 5 to 35% by weight of the film, preferably 7 to 30% by weight and particularly preferably 9 to 25% by weight, of a high polymer, the high polymer being an amorphous high polymer having a higher glass transition point than the glass transition temperature of the linear polyester and/or a crystalline high polymer having a higher melting point than the glass transition temperature of the linear polyester.

According to a seventh embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film is usable as a synthetic paper.

According to an eighth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the pattern is a watermark.

According to a ninth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the pattern is detectable by touch.

According to a tenth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the pattern is detectable by change in gloss.

According to an eleventh embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film is white i.e. non-transparent axially stretched self-supporting film providing the background from the pattern is white.

According to a twelfth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film is coloured.

According to a thirteenth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further contains at least one colorant.

According to a fourteenth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film is exclusive of foaming agent and/or decomposition products of a foaming agent.

The permanent transparent pattern can itself represent an image or the non-transparentized area of the film can represent an image. The permanent transparent pattern can, for example, be part of a banknote, a share certificate, a ticket, a credit card, an identity card, an identity document or a label for luggage and packages and be one of a large number of security features rendering falsification as difficult as possible. Such additional security features include security printing, holograms, luminescing beads and luminescing threads. The permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film can be one of the foils comprised in multiplex laminate.

Non-Transparent Microvoided Axially Stretched Film

According to a first embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, used in producing the permanent transparent pattern according to the present invention, the film further comprises at least one inorganic opacifying pigment.

According to a second embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, used in producing the permanent transparent pattern according to the present invention, the film further comprises at least one inorganic opacifying pigment selected from the group consisting of silica, zinc oxide, zinc sulphide, lithopone, barium sulphate, calcium carbonate, titanium dioxide and clays.

According to a third embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, the film comprises a continuous phase linear polyester matrix having dispersed therein from 5 to 35% by weight, preferably 7 to 30% by weight and particularly preferably 9 to 25% by weight, of the film of a high polymer, the high polymer being an amorphous high polymer having a higher glass transition point than the glass transition temperature of the linear polyester and/or a crystalline high polymer having a higher melting point than the glass transition temperature of the linear polyester.

According to a fourth embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, used in producing the permanent transparent pattern according to the present invention, the film further comprises ≦5% by weight of inorganic opacifying pigment each with a refractive index of less than 2.0.

According to a fifth embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, the film comprises a polymer as a continuous phase and dispersed uniformly therein an amorphous high polymer with a higher glass transition temperature than the glass transition temperature of the continuous phase and/or a crystalline high polymer with a melting point higher than the glass transition phase of the continuous phase and inorganic opacifying pigment as particles all having a refractive index of at least 2.0 in a total concentration of between 0.5 and 5% by weight of the film.

According to a sixth embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, used in producing the permanent transparent pattern according to the present invention, the film is a biaxially stretched film.

According to a seventh embodiment of the non-transparent microvoided axially-stretched self-supporting film, used in producing the permanent transparent pattern according to the present invention, the non-transparent microvoided axially stretched self-supporting polymeric film further contains ≦0.5% by weight of the film of a whitening agent.

The non-transparent microvoided axially-stretched polymeric film may further contain other ingredients such as antioxidants, light stabilizers, UV-absorbers and flame retardants.

The extruded film has a thickness of approximately 10 μm to approximately 6000 μm, with a thickness of approximately 100 to approximately 5000 μm being preferred, a thickness of approximately 200 μm to approximately 3000 μm being particularly preferred and a thickness of approximately 500 μm to approximately 2000 μm being especially preferred.

The non-transparent microvoided axially-stretched polymeric film is produced by orienting the film by stretching e.g. in the machine direction or in a direction perpendicular to the machine direction (the transversal direction). Preferably the non-transparent microvoided axially-stretched film is biaxially stretched. Biaxial stretching is realized by orienting the film by first stretching in one direction (e.g. in the machine direction=MD) and then stretching in a second direction [e.g. perpendicularly to the machine direction=TD (transversal direction)]. This orients the polymer chains thereby increasing the density and crystallinity. Longitudinal orientation can be carried out with the aid of two rolls running at different speeds corresponding to the desired stretching ratio by setting the surface speed V2 of the rotating rollers relative to the extrusion speed V1 so that the stretching ratio is V2/V1. The longitudinal stretching ratio should be sufficient to create voids.

Any longitudinal stretching operations known in the art to produce axially and biaxially oriented polyester film may be used. For instance, the combined film layers are passed between a pair of infra red heaters which heats the layers to a temperature above the glass transition temperature of the polyester (about 80° C. for polyethylene terephthalate) in the region where the stretching occurs. The temperatures at which stretching is carried out should be close to the glass transition temperature of the continuous phase polymer in order to improve opacity. Furthermore, the stretching temperatures should be below the glass transition temperature of the amorphous high polymer or melting point of the crystalline high polymer. In the case of polyethylene terephthalate, the longitudinal stretching is generally carried out at from about 80 to about 130° C. During longitudinal stretching opacity is realized as a result of the voids produced in the film extending longitudinally from each particle of dispersed polymer.

Transverse stretching is carried out at an angle substantially 90° to the direction of longitudinal stretching, with the angle being typically between about 70° and 90°. For transverse stetching use is generally made of an appropriate tenter frame, clamping both edges of the film and then drawing toward the two sides by heating the axially stretched film optionally with at least one primer layer thereon by, for example, passing through hot air heaters which heat the film above the glass transition temperature of the continuous phase. Transverse stretching at or below 30° C. above the glass transition temperature of the continuous phase, with a temperature at or below 20° C. above the glass transition temperature of the continuous phase preferred and a temperature at or below 10° C. above the glass transition temperature of the continuous phase being particularly preferred. In the case of polyethylene terephthalate and its copolymers, the transverse stretching is carried out at from about 80 to about 170° C., with from about 90 to about 160° C. being preferred and from about 85 to about 150° being particularly preferred. The transverse stretching of the film causes the voids to extend transversely.

The production of the biaxially stretched polymeric film, according to the present invention, is preferably produced by longitudinally stretching the thick film at a stretching tension >2.5 N/mm², with a stretching tension >5.0 N/mm² being preferred and a stretching tension >7.0 N/mm² being particularly preferred. After optional intermediate quenching the longitudinal stretching is followed by transverse stretching at an angle substantially 90° to the first stretching process to at least twice the initial length at a stretching tension of >2.5 N/mm², with a stretching tension of >4.0 N/mm² being preferred, at a temperature preferably at or below 30° C. above the glass transition temperature of the continuous phase and preferably at or below 20° C. above the glass transition temperature of the continuous phase. The realizable stretching tension increases with decreasing stretching temperature.

Longitudinal and transverse stretching may be performed simultaneously e.g. with an apparatus produced by Brückner.

The production process may further comprise, as a further step, a thermal fixation step to counter shrinkage.

The longitudinal stretching ratio is generally in the range from about 2 to about 6, with a range from about 2.5 to about 5 being preferred and a range from about 3 to about 4 being particularly preferred. The high the stretching ratio, the higher the opacity.

The optional transverse stretching ratio is generally in the range from about 2 to about 6, with a range from about 2.5 to about being preferred and a range from about 3 to about 4 being particularly preferred. The opacity increases at higher stretching rates and also at lower transverse stretching temperatures.

The axially or biaxially stretched film is passed through a second set of hot air heaters which blow hot air at a temperature of between 160 and 240° C. onto the film layers to heat-set or thermofix the film layers. The heat-set temperature must be sufficient to obtain crystallization of the polyester but care must be taken not to overheat the layers since the voids can collapse. On the other hand increasing the heat-set temperature improves the dimensional stability of the film. An appropriate mix of properties can be obtained by varying the heat-set temperature. The preferred heat-set or thermofixation temperature in the case of polyethylene terephthalate is at least 140° C. and preferably at least 150° and particularly preferably at least 175° C.

According to an eighth embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, used in producing the permanent transparent pattern according to the present invention, the non-transparent microvoided axially stretched self-supporting polymeric film is provided with a subbing layer.

Before or after longitudinal stretching a first subbing layer, called a primer layer, may be applied to the non-voided polyester layer by a coating means such as an air knife coating system. The first subbing layer is for example formed from a (meth)acrylate copolymer, a poly(meth)acrylate, a polyurethane, a sulphonated polyester, a styrene-(meth)acrylate copolymer or a chloride containing copolymer such as vinylidene chloride copolymer in latex form having some hydrophilic functionality through the presence of a copolymerized unsaturated carboxylic acid which is applied as an aqueous dispersion.

According to a ninth embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, used in producing the permanent transparent pattern according to the present invention, the non-transparent microvoided axially stretched self-supporting polymeric film is provided with at least one of alphanumeric characters, an embossed pattern, an optionally embossed hologram, a continuous image, a half-tone image and a digital image.

According to a tenth embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, used in producing the permanent transparent pattern according to the present invention, the film is provided on at least one side with a transparent or translucent overprintable layer i.e. suitable for impact or non-impact printing. This transparent overprintable layer can be provided over at least one of alphanumeric characters, an embossed pattern, an optionally embossed hologram, a continuous image, a half-tone image and digital image on a surface of the non-transparent microvoided axially stretched self-supporting polymeric film.

According to an eleventh embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, used in producing the permanent transparent pattern according to the present invention, the film is provided on at least one side with a transparentizable porous overprintable layer i.e. suitable for impact or non-impact printing e.g. ink-jet printing. Transparentizable porous layers transparentized by the application of a liquid with an appropriate refractive index, which can also be applied image-wise, are as disclosed in EP-A 1 362 710 and EP-A 1 398 175. This transparentizable overprintable layer can be provided over at least one of alphanumeric characters, an embossed pattern, an optionally embossed hologram and a continuous, half-tone or digital image on a surface of the non-transparent microvoided axially stretched self-supporting polymeric film with a permanent transparent pattern.

Transparentization of part of the transparentizable porous receiving layer can itself produce an image or the non-transparentized area of the opaque porous receiving layer can itself represent an image. The permanent transparent pattern can, for example, be part of a banknote, a share certificate, a ticket, a credit card, an identity document or a label for luggage and packages.

According to a twelfth embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, used in producing the permanent transparent pattern according to the present invention, the non-transparent microvoided axially stretched self-supporting polymeric film has a thickness in the range from about 15 μm to about 500 μm, with from about 25 μm to about 300 μm being preferred, from about 50 μm to about 200 μm being particularly preferred and from about 75 to about 150 μm being expecially preferred.

The non-transparent microvoided axially stretched self-supporting polymeric film, used in the present invention, can be produced by a process comprising the steps of: i) mixing a linear polyester, a high polymer being an amorphous high polymer having a glass transition temperature higher than the glass transition temperature of the linear polyester and/or a crystalline high polymer having a melting point higher than the glass transition temperature of the linear polyester, optionally together with ≦3% by weight of the film of an inorganic opacifying pigment and also optionally together with ≦0.5% by weight of the film of a whitening agent in a kneader or an extruder, ii) forming the mixture produced in step i) in a thick film followed by quenching to room temperature, iii) longitudinally stretching the thick film at a stretching tension of >2.5 N/mm² at a temperature between the glass transition temperature of the amorphous high polymer and the glass transition temperature of the linear polyester or between the melting temperature of the crystalline high polymer and the glass transition temperature of the linear polyester to at least twice the initial length and iv) optionally laterally stretching the thick film at a stretching tension of >2.5 N/mm² at a temperature between the glass transition temperature of the amorphous high polymer and the glass transition temperature of the linear polyester or between the melting temperature of the crystalline high polymer and the glass transition temperature of the linear polyester to at least twice the initial length. Steps iii) and iv) of this process can be performed simultaneously and the process may further comprise a thermal relaxation step.

Before or after longitudinal stretching a first priming layer, otherwise known as a subbing layer or a primer layer, may be applied to the non-voided polyester layer by a coating means such as an air knife coating system. The first subbing layer is for example formed from a (meth)acrylate copolymer, a poly(meth)acrylate, a poly-urethane, a sulphonated polyester or a chloride containing copolymer such as vinylidene chloride copolymer in latex form having some hydrophilic functionality through the presence of a copolymerized unsaturated carboxylic acid which is applied as an aqueous dispersion. Alternatively layers of adhesive may be applied by coating, printing e.g. gravure printing or lamination.

Optical Density of the Film Due to Microvoids

The optical density of the film measured in transmission with a visible filter due to microvoids is obtained by measuring the optical density of the film without void-producing ingredients as a function of film thickness to provide comparative values. The optical density of a film measured in transmission with a visible filter due to voids is then obtained by biaxially stretching a composition to which has been added the void-inducing ingredient and subtracting the measured optical density measured in transmission with a visible filter from the optical density measured in transmission with a visible filter for the film composition without void-inducing ingredient for the film thickness expected on the basis of the longitudinal and transverse drawing ratios.

Polyolefin

According to a fifteenth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film comprises a polyolefin as continuous phase.

According to a sixteenth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film comprises polypropylene or poly(4-methylpentene) as continuous phase.

Linear Polyester

According to a seventeenth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film comprises a linear polyester as continuous phase, the linear polyester preferably comprising at least one aromatic polyester resin. Upon heating, e.g. during mixing in an extruder, the different linear polyester resins present will undergo metathesis, condensing and decondensing so as to evolve upon sufficiently long heating into a single resin.

According to an eighteenth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester having monomer components consisting essentially of at least one aromatic dicarboxylic acid and at least one aliphatic diol.

If the continuous phase of the microvoided film is a polyester matrix, it can comprise any polyester and preferably comprises poly(ethylene terephthalate) or a copolymer thereof. Suitable polyesters include those produced from aromatic, aliphatic, or cyclo-aliphatic dicarboxylic acids or their esters, the dicarboxylate group having 4-20 carbon atoms, and aliphatic (including alicyclic) glycols or ethers thereof, the aliphatic dimethylene groups having 2-24 carbon atoms, and mixtures thereof. Examples of suitable aromatic dicarboxylates include terephthalate, isophthalate, phthalate, naphthalene dicarboxylates and sodiosulfoisophthalate. Examples of suitable aliphatic dicarboxylates include succinate, glutarate, adipate, azelaiate (from azelaic acid), sebacate, fumarate, maleiate (from maleic acid) and itaconate. Examples of suitable alicylic dicarboxylate are 1,4-cyclohexane-dicarboxylate, 1,3-cyclohexane-dicarboxylate and 1,3-cyclopentane-dicarboxylate. Examples of suitable aliphatic dimethylenes include ethylene, propylene, methylpropylene, tetramethylene, pentamethylene, hexamethylene, neopentylene [—CH₂C(CH₃)₂—CH₂], 1,4-cyclohexane-dimethylene, 1,3-cyclohexane-dimethylene, 1,3-cyclopentane-dimethylene, norbornane-dimethylene, —CH₂CH₂(OCH₂CH₂)_(n)—, where n is an integer with 1 to 5 being preferred, and mixtures thereof.

Such polyesters are well known in the art and may be produced by well-known techniques, for example, those described in U.S. Pat. No. 2,465,319 and U.S. Pat. No. 2,901,466.

Preferred continuous matrix polymers are those having repeat units from terephthalic acid or naphthalene dicarboxylic acid and at least one glycol selected from ethylene glycol, 1,4-butanediol, neopentyl glycol, 2-endo,3-endo norbornane dimethanol and 1,4-cyclohexanedimethanol. Poly(ethylene terephthalate), which may be modified by small amounts of other monomers, is especially preferred. Other suitable polyesters include liquid crystal copolyesters formed by the inclusion of a suitable amount of a co-acid component such as stilbene dicarboxylic acid. Examples of such liquid crystal copolyesters are those disclosed in U.S. Pat. No. 4,420,607, U.S. Pat. No. 4,459,402 and U.S. Pat. No. 4,468,510.

According to a nineteenth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched film according to the present invention, the film has as continuous phase a linear polyester having a number average molecular weight in the range of 10,000 to 30,000.

According to a twentieth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester having an inherent viscosity determined in a 0.5 g/dL solution of 60 wt % phenol and 40 wt % ortho-dichlorobenzene at 25° C. of at least 0.45 dl/g with an inherent viscosity of 0.48 to 0.9 dl/g being preferred, an inherent viscosity of 0.5 to 0.85 dl/g being particularly preferred and an inherent viscosity of 0.55 to 0.8 dl/g being especially preferred.

According to a twenty-first embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester comprising poly(ethylene terephthalate) or a copolymer thereof.

According to a twenty-second embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester comprising at least one aromatic polyester having aromatic dicarboxylate monomer units selected from the group consisting of terephthalate, isophthalate and naphthalene dicarboxylates.

According to a twenty-third embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester in which at least 1 mole % of the aromatic dicarboxylate monomer units in the linear polyester are isophthalate monomer units, with at least 3 mole % being preferred and at least 5 mole % being particularly preferred.

According to a twenty-fourth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester in which 30 mole % or less of the aromatic dicarboxylate acid monomer units in the linear polyester are isophthalate monomer units, with 20 mole % or less being preferred, 18 mole % or less being particularly preferred and 15% or less being especially preferred.

According to a twenty-fifth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester in which the aliphatic dimethylene monomer units are selected from the group consisting of ethylene, tetramethylene and 1,4-cyclohexane-dimethylene.

According to a twenty-sixth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester comprising at least 1 mole % of the aliphatic dimethylene monomer units in the linear polyester are neopentylene or 1,4-cyclohexanedimethylene monomer units, with at least 3 mole % being preferred and at least 5 mole % being particularly preferred.

According to a twenty-seventh embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester comprising 30 mole % or less of the aliphatic dimethylene monomer units in the linear polyester are neopentylene or 1,4-cyclohexanedimethylene monomer units, with 20 mole % or less being preferred, 18 mole % or less being particularly preferred and 15% or less being especially preferred.

According to a twenty-eighth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester further comprising an electroconductivity enhancing additive e.g. a metallic salt which ionizes in the melt giving enhanced electroconductivity such as magnesium acetate, manganese salts and cobalt sulphate. Suitable salt concentrations are about 3.5×10⁻⁴ moles/mole polyester. Enhanced polyester melt viscosity enables improved pinning of the melt on the chilling roller maintained at a temperature of 5 to 25° C. (preferably 15 to 30° C.) to cool the extrudate thereby enabling higher stretching forces to be realized and hence enhanced void-forming and a higher degree of opacification.

According to a twenty-ninth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester having a glass transition temperature from 40 to 150° C., preferably from 50 to 120° C. and particularly preferably from 60 to 100° C.

According to a thirtieth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester which is orientable.

According to a thirty-first embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has as continuous phase a linear polyester blend comprising poly(ethylene terephthalate) and poly(1,4-cyclohexylene dimethylene terephthalate).

Amorphous High Polymer

The amorphous high polymer used in the non-transparent microvoided axially stretched self-supporting polymeric film, used in the present invention, has a glass transition temperature higher than the glass transition temperature of the continuous phase in which it is dispersed e.g. a linear polyester. Poly(ethylene terephthalate), for example, has a glass transition temperature of ca 80° C.

The glass transition temperatures and refractive indices for various amorphous high polymers are given in the table below:

Refractive index for sodium T_(g) line at 589.3 nm [° C.] [ASTM D642] polystyrene 100 1.57-1.60 poly-α-methyl-styrene 168 1.610 poly-4-methyl-styrene 93 — poly-α-vinyl-naphthalene 159  1.6818 polyacrylonitrile 85 1.514, 1.5187 polymethacrylonitrile 120 1.520 polymethyl methacrylate 105 1.49, 1.4893 polyacrylamide 165 — copolymer of acrylonitrile and styrene 112 1.56-1.57, 1.57 copolymer of 28.5 wt % acrylonitrile and 108 1.56-1.57, 1.57 71.5 wt % styrene ABS 110 1.53-1.54

According to a thirty-second embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein is an amorphous high polymer which is at least partially crosslinked e.g. at least partially crosslinked poly(methyl methacrylate) or at least partially crosslinked copolymers of acrylonitrile and styrene.

According to a thirty-third embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein is an amorphous high polymer having a degree of crosslinking of at least 10%.

According to a thirty-fourth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein is an amorphous high polymer comprising at least one chain-polymerized block.

According to a thirty-fifth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein is an amorphous high polymer selected from the group consisting of a polymethylmethacrylate, a SAN polymer, and a copolymer of acrylonitrile, butadiene and styrene.

According to a thirty-sixth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein is an amorphous high polymer comprising at least one chain-polymerized block and the at least one chain-polymerized block is selected from the group consisting of polystyrene, styrene copolymers, SAN-polymers, polyacrylates, acrylate-copolymers, polymethacrylates and methacrylate-copolymers.

According to a thirty-seventh embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein is an amorphous high polymer comprising at least one chain-polymerized styrene copolymer block selected from the group consisting of SAN-polymers, ABS-polymers and SBS-polymers.

The SAN polymer additive of the present composition is a known class of polymer consisting essentially of a random copolymer of a styrenic monomer component, including styrene as well as an alpha-lower alkyl-substituted styrene or mixtures thereof and an acrylonitrilic monomer component including acrylonitrile as well as an alpha-lower alkyl substituted acrylonitrile or mixtures thereof. By lower-alkyl is meant a straight or branched chain alkyl group of 1 to 4 carbon atoms exemplified by the methyl, ethyl, isopropyl and t-butyl groups. In readily available SAN polymers, the styrene component is generally styrene, alpha-straight chain alkyl substituted styrene, typically alpha-methyl-styrene, or mixtures thereof with styrene being preferred. Similarly in the readily available SAN polymers, the acrylonitrile component is generally acrylonitrile, alpha-methyl-acrylonitrile or mixtures thereof with acrylonitrile being preferred.

In the SAN polymer the styrene component is present in a major weight proportion, i.e. in a weight proportion of greater than 50%, typically about 65% to about 90%, especially about 70% to about 80%, based on the combined weight of the styrene component and the acrylonitrile component. The acrylonitrile component is present in a minor proportion, i.e. in a weight proportion of less than 50%, typically about 10% to about 35% especially about 20% to 30% based on the combined weight of the styrene monomer component and the acrylonitrile monomer component. Styrene-acrylonitrile copolymers are currently commercially available with an acrylonitrile content of 15 to 35% by weight, with 18 to 32% by weight being preferred and 21 to 30% by weight being particularly preferred.

The SAN polymer class is more particularly identified and described in R. E. Gallagher, U.S. Pat. No. 3,988,393, issued Oct. 26, 1976 (especially at Column 9, lines 14-16 and in claim 8), in “Whittington's Dictionary of Plastics”, Technomic Publishing Co., First Edition, 1968, page 231, under the section headed “Styrene-Acrylonitrile Copolymers (SAN)”, and R. B. Seymour, “Introduction to Polymer Chemistry”, McGraw-Hill, Inc., 1971, page 200, (last two lines) to page 201 (first line). The preparation of a SAN polymer by copolymerization of styrene and acrylonitrile is more particularly described in the “Encyclopedia of Polymer Science and Technology”, John Wiley and Sons, Inc., Vol. 1, 1964, pages 425-435.

According to a thirty-eighth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein is a SAN polymer.

According to a thirty-ninth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein is a SAN polymer having a concentration of AN-monomer units of 15 to 35% by weight.

According to a fortieth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein is a SAN polymer in a concentration of at least 5% by weight of the film, with at least 10% by weight of the film being preferred and at least 12% by weight being particularly preferred.

According to a forty-first embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein is a SAN polymer in a concentration of 35% by weight or less with a concentration of 25% by weight or less being preferred and a concentration of 20% by weight or less being particularly preferred.

According to a forty-second embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein is a non-crosslinked SAN polymer having a number average molecular weight in the range of 30,000 to 100,000, preferably in the range of 32,000 to 80,000, particularly preferably in the range of 35,000 to 70,000 and especially preferably in the range of 40,000 to 60,000. Typical SAN-polymers have number averaged molecular weights of 45,000 to 54,000 and polymer dispersities (M_(w)/M_(n)) of 1.2 to 2.5.

According to a forty-third embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein is a non-crosslinked SAN polymer having a weight average molecular weight in the range of 50,000 to 200,000, preferably in the range of 75,000 to 150,000. The higher the molecular weight of the SAN polymer, the larger the size of the dispersed SAN polymer particles.

According to a forty-fourth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein are amorphous high polymer particles having a diameter of less than 10 μm, with particles having a number average particle size of 0.5 to 5 μm being preferred and particles with an average particle size of 1 to 2 μm being particularly preferred. The smaller the particles size, the higher the opacity.

According to a forty-fifth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film is exclusive of a polyether such as polyethylene oxide. Such polyethers decrease the density and may decompose producing additional non-uniformly distributed voids.

According to a forty-sixth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film is exclusive of a cellulose ester.

Crystalline High Polymer

The crystalline high polymer used in the non-transparent microvoided axially stretched self-supporting polymeric film, used in the present invention, has a melting point higher than the glass transition temperature of the continuous phase polymer in which it is dispersed e.g. a linear polyester. Crystalline high polymers with sufficiently high melting points include polyethylene, polypropylene and poly(4-methyl-1-pentene).

According to a forty-seventh embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein are crystalline high polymer particles having a number averaged particle size of 0.5 to 12 μm, with 1 to 7 μm being preferred and 2 to 5 μm being particularly preferred.

According to a forty-eighth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film has a linear polyester as continuous phase and dispersed therein are crystalline high polymer particles selected from polyethylene, polypropylene and poly(4-methyl-1-pentene) particles, with poly(4-methyl-1-pentene) particles being preferred.

The melting points and refractive indices for various polyethylenes and polypropylenes are given in the table below:

Refractive index for sodium line at 589.3 nm T_(m) [° C.] [ASTM D642] polyethylene 95 1.51-1.54 high density polyethylene 141 1.51-1.54 isotactic polypropylene 165 1.49 syndiotactic polypropylene 189 1.49 polypropylene (atactic) 1.4735 Poly(4-methylpentene) 235 1.4630

Inorganic Opacifying Pigment

According to a forty-ninth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, wherein the film further comprises at least one inorganic opacifying pigment.

According to a fiftieth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises ≦5% by weight of inorganic opacifying pigment each with a refractive index of less than 2.0, with less than ≦3% by weight of inorganic opacifying pigment each with a refractive index of less than 2 being preferred.

According to a fifty-first embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises ≦5% by weight of inorganic opacifying pigment with less than ≦3% by weight being preferred.

According to a fifty-second embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film comprises a polymer as a continuous phase and dispersed uniformly therein an amorphous high polymer with a higher glass transition temperature than the glass transition temperature of the continuous phase and/or a crystalline high polymer with a melting point higher than the glass transition phase of the continuous phase and inorganic opacifying pigment as particles all having a refractive index of at least 2.0 in a total concentration of between 0.5 and 5% by weight of the film.

According to a fifty-third embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, wherein the film further comprises at least one inorganic opacifying pigment and the concentration of inorganic opacifying pigment is ≧1% by weight.

According to a fifty-fourth embodiment of the non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises an inorganic opacifying pigment having a number averaged particle size of 0.1 to 10 μm, with 0.2 to 2 μm being preferred and 0.2 to 1 μm being particularly preferred.

According to a fifty-fifth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises an inorganic opacifying pigment selected from the group consisting of silica, zinc oxide, zinc sulphide, lithopone, barium sulphate, calcium carbonate, titanium dioxide, aluminium phosphates and clays. The titanium dioxide may have an anatase or rutile morphology and may be stabilized by alumina oxide and/or silicon dioxide. The aluminium phosphate can be an amorphous hollow pigment e.g. the Biphor™ pigments from BUNGE.

The refractive indices of these pigments are given in the table below:

refractive index for inorganic opacifying pigment sodium line at 589.3 nm kaolinite 1.53-1.57 bentonite  1.557 china clay 1.56 silica-silica gel 1.55 silica-cristobalite 1.487, 1.484 silica-quartz 1.544, 1.553 calcium carbonate 1.59, 1.6, 1.58 calcium carbonate-calcite 1.486, 1.64-1.66 barium sulphate-baryte 1.637, 1.638, 1.649, 1.64 Lithopone 30% (zinc sulphide/ 1.84 barium sulphate) zinc oxide (ultrafine) 1.9  zinc oxide (zincite) 2.008, 2.029 zinc sulphide 2.37 titanium dioxide-anatase 2.554, 2.493, 2.55 titanium dioxide-rutile 2.616, 2.903, 2.76

Addition of an inorganic opacifying pigment has the advantage of stabilizing the orientation of the polyester, so that the non-transparent microvoided axially stretched self-supporting polymeric film can be stabilized at temperatures of 175° C. without substantially affecting the opacity of the non-transparent microvoided axially stretched self-supporting polymeric film. Without the presence of an inorganic opacifying pigment, such as BaSO₄, thermofixing of the polyester is possible, but only at the expense of some of the opacity of the non-transparent microvoided axially stretched self-supporting polymeric film. Moreover, pigments with a refractive index below 2.0 do not of themselves provide substantial opacity due to the small refractive index differences between the pigment and the polymer matrix.

Titanium dioxide particles dispersed in polymer films have been found not to induce microvoiding upon stretched the films.

Whitening Agent

According to a fifty-sixth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises a whitening agent, preferably in a concentration of ≦0.5% by weight of the film, with ≦0.1% by weight being preferred, ≦0.05% by weight being particularly preferred and ≦0.035% by weight being especially preferred.

According to a fifty-seventh embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises a whitening agent selected from the group consisting of bis-benzoxazoles e.g. bis-benzoxazolyl-stilbenes and bis-benzoxazolyl-thiophenes; benzotriazole-phenylcoumarins; naphthotriazole-phenylcoumarins; triazine-phenylcoumarins and bis(styryl)biphenyls.

According to a fifty-eighth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises a whitening agent in a concentration of <0.1% by weight and preferably <0.05% by weight.

Suitable whitening agents are:

UVITEX ® OB CIBA UVITEX ® OB-ONE CIBA Eastobrite OB 2,5-thiophenediylbis(5-tert-butyl- Eastman 1,3-benzoxazole) Chemical bis-benzoxazolyl-stilbene bis-benzoxazolyl-thiophene

Flame Retardant

According to a fifty-ninth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises a flame retardant.

According to a sixtieth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises a flame retardant selected from the group consisting of: brominated compounds; organophosphorus compounds; melamine; melamine-derivatives, e.g. melamine salts with organic or inorganic acids such as boric acid, cyanuric acid, phosphoric acid or pyro/poly-phosphoric acid, and melamine homologues such as melam, melem and melon; metal hydroxides e,g. aluminium hydroxide and magnesium hydroxide; ammonium polyphosphates and zinc borate e.g. with a composition of xZnO.yB₂O₃.zH₂O such as 2ZnO.3B₂O₃.3.5H₂O.

Suitable flame retardants include:

SAYTEX ® HP-7010 P/G brominated polystyrene Albemarle Corporation SAYTEX ® HP-3010 brominated polystyrene Albemarle Corporation SAYTEX ® 8010 ethane-1,2-bis(pentabromophenyl) Albemarle Corporation SAYTEX ® BT-93 ethylene bis-tetrabromo- Albemarle Corporation phthalimide SAYTEX ® BT-93W ethylene bis-tetrabromo- Albemarle Corporation phthalimide SAYTEX ® CP-2000 brominated compound Albemarle Corporation SAYTEX ® 120 tetradecabromo-diphenoxy benzene Albemarle Corporation SAYTEX ® 102E Decabromodiphenyl oxide Albemarle Corporation SAYTEX ® 9006L brominated compound Albemarle Corporation SAYTEX ® HP-900 brominated compound Albemarle Corporation SAYTEX ® HP-800A brominated compound Albemarle Corporation SAYTEX ® HP-800AG brominated compound Albemarle Corporation SAYTEX ® BC70HS brominated compound Albemarle Corporation NcendX P-30 organophosphorus compound Albemarle Corporation MARTINAL ® OL-104 aluminium hydroxide Albemarle Corporation MARTINAL ® OL-104/LE aluminium hydroxide Albemarle Corporation MARTINAL ® OL-104/WE aluminium hydroxide Albemarle Corporation MARTINAL ® OL-104/LFF aluminium hydroxide Albemarle Corporation MARTINAL ® OL-104/LCD aluminium hydroxide Albemarle Corporation MARTINAL ® OL-107 aluminium hydroxide Albemarle Corporation MARTINAL ® OL-107/LE aluminium hydroxide Albemarle Corporation MARTINAL ® OL-107/LFF aluminium hydroxide Albemarle Corporation MARTINAL ® OL-107/LCD aluminium hydroxide Albemarle Corporation MARTINAL ® OL/Q-107 aluminium hydroxide Albemarle Corporation MARTINAL ® OL-111/LE aluminium hydroxide Albemarle Corporation MAGNIFIN ® H3 magnesium hydroxide Albemarle Corporation MAGNIFIN ® H5 magnesium hydroxide Albemarle Corporation MAGNIFIN ® H7 magnesium hydroxide Albemarle Corporation MAGNIFIN ® H10 magnesium hydroxide Albemarle Corporation MAGNIFIN ® T2C magnesium hydroxide Albemarle Corporation MAGNIFIN ® T3C magnesium hydroxide Albemarle Corporation MELAPUR ® MCXL melamine cyanurate CIBA MELAPUR ® MC50 melamine cyanurate CIBA MELAPUR ® MC25 melamine cyanurate CIBA MELAPUR ® 200 70 melamine polyphosphate CIBA MELAPUR ® MP melamine phosphate CIBA FIREBRAKE ® ZB a zinc borate compound LUZENAC FIREMASTER ® PBS-64 brominated styrene-based GREAT LAKES CHEMICAL technology CORP. FIREMASTER ® PBS-64HW brominated styrene-based GREAT LAKES CHEMICAL technology CORP. FIREMASTER ® CP-44B copolymer of brominated styrene GREAT LAKES CHEMICAL & glycidyl methacrylate CORP.

Antioxidant

According to a sixty-first embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises an antioxidant.

According to a sixty-second embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises an antioxidant selected for the group consisting of organotin derivatives, sterically hindered phenols, sterically hindered phenol derivatives and phosphites.

Suitable antioxidants include:

ETHANOX ® 310 Organotin catalyzed pentaerythritol Albemarle Corporation tetrakis (3-(3,5-di-t-butyl-4- hydroxyphenyl)-propionate) ETHANOX ® 310TF “Tin-free” pentaerythritol tetrakis Albemarle Corporation (3-(3,5-di-t-butyl-4-hydroxyphenyl)- propionate) ETHANOX ® 314 1,3,5-tris(3,5-di-t-butyl-4-hydroxy- Albemarle Corporation benzyl)-1,3,5-triazine- 2,4,6(1h,3h,5h)-trione ETHANOX ® 330 1,3,5-trimethyl-2,4,6-tris (3,5-di- Albemarle Corporation tert-butyl-4-hydroxy-benzyl) benzene ETHANOX ® 376 octadecyl-3-(3,5-di-t-butyl-4- Albemarle Corporation hydroxyphenyl)-propionate ETHAPHOS ® 368 tris-(2,4-di-t-butylphenyl) phosphite Albemarle Corporation ETHAPHOS ® 326 Bis (2,4-di-t-butylphenyl) Albemarle Corporation pentaerythritol diphosphite IRGANOX ® 259 CIBA IRGANOX ® 1010 CIBA IRGANOX ® 1425 CIBA IRGANOX ® B 900 CIBA HOSTANOX ® O 3 Bis[3,3′-bis-(4′-hydroxy-3′-t-butyl- CLARIANT phenyl)butanoic acid]glycol ester HOSTANOX ® tetrakis[methylene(3,5-di-t-butyl-4- CLARIANT O 10 hydroxy-benzyl)isocyanurate HOSTANOX ® 1/1 mixture of HOSTANOX ® O 10 & CLARIANT O 310 HOSTANOX ® O 3 HOSTANOX ® 245 ethylene bis(oxyethylene)bis-[3-(5-t- CLARIANT butyl-4-hydroxy-m-tolyl)-propionate]

Light Stabilizers

According to a sixty-third embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises a light stabilizer.

According to a sixty-fourth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises a hindered amine light stabilizer.

Suitable light stabilizers include:

LS-01 CHIMASSORB 119 CIBA LS-02 CHIMASSORB 944 CIBA LS-03 TINUVIN ® 123 CIBA LS-04 TINUVIN ® 144 CIBA LS-05 TINUVIN ® 622 CIBA LS-06 TINUVIN ® 765 CIBA LS-07 TINUVIN ® 770 CIBA LS-08 TINUVIN ® 783 CIBA LS-09 TINUVIN ® 791 CIBA LS-10 TINUVIN ® B 75 CIBA LS-11 TINUVIN ® B 241 CIBA

UV-Absorbers

According to a sixty-fifth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises a UV-absorber.

According to a sixty-sixth embodiment of the permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film, according to the present invention, the film further comprises an UV-absorber selected from the group consisting of benzotriazole derivatives and triazines derivatives.

Suitable UV-absorbers include:

UV-01 CHIMASSORB CIBA UV-02 TINUVIN ® 213 CIBA UV-03 TINUVIN ® 234 CIBA UV-04 TINUVIN ® 327 CIBA UV-05 TINUVIN ® 360 CIBA UV-06 TINUVIN ® 1577 CIBA UV-07 HOSTAVIN ® PR-25 propanedioic acid,[(4-methoxy-phenyl)- CLARIANT methylene]-, dimethyl ester UV-08 SANDUVOR ® VSU 2-ethyl-2′-ethoxy-oxalanilide CLARIANT UV-09 HOSTAVIN ® B-CAP tetra-ethyl-2,2′-(1,4-phenylene- CLARIANT dimethylidene)-bismalonate UV-10 HOSTAVIN ® ARO 8 2-hydroxy-4-n-octyloxybenzophenone CLARIANT

Layer Configuration

Aspects of the present invention are realized by a layer configuration comprising the non-transparent microvoided axially stretched self-supporting polymeric film exclusive of foam with a permanent transparent pattern, according to the present invention.

According to a first embodiment of the layer configuration, according to the present invention, the film is exclusive of foaming agent and/or decomposition products of a foaming agent.

According to a second embodiment of the layer configuration, according to the present invention, a surface of the non-transparent microvoided axially stretched self-supporting polymeric film with a permanent transparent pattern is provided with a subbing layer. This subbing layer makes it possible to improve wettability and adhesive property of the polymeric film and preferably comprises a polyester resin, a polyurethane resin, a poly(ester urethane) resin or an acrylic resin.

According to a third embodiment of the layer configuration, according to the present invention, a surface of the non-transparent microvoided axially stretched self-supporting polymeric film with a permanent transparent pattern is provided with at least one of alphanumeric characters, an embossed pattern, an optionally embossed hologram and a continuous, half-tone or digital image.

According to a fourth embodiment of the layer configuration, according to the present invention, the film with a permanent transparent pattern is provided on at least one side with a transparent overprintable layer i.e. suitable for impact or non-impact printing. This transparent overprintable layer can be provided over at least one of alphanumeric characters, an embossed pattern, an optionally embossed hologram and a continuous, half-tone or digital image on a surface of the non-transparent microvoided axially stretched self-supporting polymeric film with a permanent transparent pattern. Moreover, at least one of alphanumeric characters, an embossed pattern, an optionally embossed hologram and a continuous, half-tone or digital image can also be provided under this transparent overprintable layer by a process subsequent to the provision of the overprintable layer.

According to a fifth embodiment of the layer configuration, according to the present invention, the film with a permanent transparent pattern is provided on at least one side with a transparentizable overprintable layer i.e. suitable for impact or non-impact printing e.g. ink-jet printing. Transparentizable porous layers transparentized by the application of a liquid with an appropriate refractive index, which can also be applied image-wise, are as disclosed in EP-A 1 362 710 and EP-A 1 398 175. This transparentizable overprintable layer can be provided over at least one of alphanumeric characters, an embossed pattern, an optionally embossed hologram and a continuous, half-tone or digital image on a surface of the non-transparent microvoided axially stretched self-supporting polymeric film with a permanent transparent pattern. Moreover, at least one of alphanumeric characters, an embossed pattern, an optionally embossed hologram and a continuous, half-tone or digital image can also be provided under this transparentizable overprintable layer by a process subsequent to the provision of the overprintable layer.

According to a sixth embodiment of the layer configuration, according to the present invention, the film with a permanent transparent pattern is provided the film is provided on at least one side with an ink-jet receiving layer. Typical receiving layers are either porous in the case of aqueous or solvent inks or pastes to enable rapid drying to the touch or are non-porous in the case of phase-change inks or curable inks e.g. radiation curable inks. Porous receiving layers typically comprise at least one pigment such as silica or alumina; at least one binder, such as an ammonium salt of a styrene-acrylate-acrylic acid terpolymer; a surfactant e.g. an anionic surfactant such as an aliphatic sulphonate; optionally a levelling agent, such as polydimethylsiloxane, and optionally a mordant.

Transparentization of part of the transparentizable porous receiving layer can itself produce an image or the non-transparentized area of the opaque porous receiving layer can itself represent an image. The permanent transparent pattern can, for example, be part of a banknote, a share certificate, a ticket, a credit card, an identity document or a label for luggage and packages. Moreover, an additional security feature can be provided by relative positioning of the transparency/watermark in the transparentized layer and the permanent transparent pattern in the support.

Security Document

Aspects of the present invention are also realized by a security document comprising a non-transparent microvoided polymeric film with a transparent pattern according to the present invention.

According to a first embodiment of the security document, according to the present invention, the security document is an identity card.

The security field encompasses not only personalized documents such as passports, driving licenses, identity cards (ID cards) and admission documents such as visa's and entry tickets, but also the authentification and identification of goods to avoid counterfeiting, tampering and fraud such as lottery tickets, share certificates, transaction documents, labels on luggage and the packaging of pharmaceuticals and high value products in general.

The term “identity card” encompasses cards requiring bearer identification and range from passports to national identity cards to establish the national identity of their civilians to cards involved in the electronic transfer of money such as bank cards, pay cards, credit cards and shopping cards to security cards authorizing access to the bearer of the card to particular areas such as a company (employee ID card), the military, a public service, the safe deposit departments of banks, etc. to social security cards to membership cards of clubs and societies.

Security documents conventionally comprise multilayered entities, the sub-layers being coatings, prints, adhesive layers and thin plastic foils. Security printing techniques are used such as offset, intaglio and screen printing.

Often the sub-elements of the final multilayer entities are produced using coatings, prints, adhesive layers and thin plastic foils by coating, printing, lamination, coextrusion and other conventional techniques and these sub-elements are laminated together to produce a final multilayered entity to which further security features may be applied.

Experiments have shown that the transparent pattern, according to the present invention, can be realized in a precursor document complete except for the provision of one or more security features or in one or more sub-elements from which the multilayered entity is produced. Furthermore, if the pattern, according to the present invention, is produced in a sub-element or even in a foil used to produce such a sub-element, subsequent lamination processes using pressure and/or heat do not degrade the pattern, according to the present invention, despite being possibly subject to multiple lamination processes e.g. lamination to an adhesive foil such as a polyethylene or PETG-foil followed by lamination of the resulting laminate with other foils thereby realizing a sub-element followed by laminating different sub-elements together to produce the precursor of a security document or the security document itself.

If the continuous phase of the axially stretched polymeric film is a polyester, the axially stretched self-supporting film including the permanent transparent pattern provided by the present invention can replace axially stretched polyester films in security document configurations without loss of mechanical functionality such as bending and wear properties. Conventional adhesive layers can be used with the axially stretched polyester fim including the permanent transparent pattern such as polyethylene, polyurethane adhesives and PETG and lamination temperatures between 120 and 150° C. can be used. Axially stretched polyester fim including the permanent transparent pattern can be laminated to axially stretched poly(ethylene terephthalate) without adhesive layer from a temperature of 180° C. and directly to PETG from a temperature of 160° C.

According to a second embodiment of the security document, according to the present invention, the axially stretched self-supporting film including the permanent transparent pattern is the outermost foil of the security document.

According to a third embodiment of the security document, according to the present invention, the axially stretched self-supporting film including the permanent transparent pattern is the outermost foil of the security document and is laminated to an adhesive foil.

Process for Obtaining a Permanent Transparent Pattern

Aspects of the present invention have been realized by a process for obtaining a permanent transparent pattern comprising the step of: image-wise application of heat optionally supplemented by the application of pressure to a non-transparent microvoided axially stretched self-supporting polymeric film exclusive of foam.

According to a first embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the film is exclusive of foaming agent and/or decomposition productions of a foaming agent.

According to a second embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the film further comprises at least one inorganic opacifying pigment.

According to a third embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the film further comprises at least one inorganic opacifying pigment is selected from the group consisting of silica, zinc oxide, zinc sulphide, lithopone, barium sulphate, calcium carbonate, titanium dioxide, aluminium phosphates and clays.

According to a fourth embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the film comprises ≦5% by weight of inorganic opacifying pigment each with a refractive index of less than 2.0 i.e. the total concentration of inorganic opacifying pigments in the film is ≦3% and all of these inorganic opacifying pigments have a refractive index of less than 2.0. One or more inorganic opacifying pigments may be present in the film.

According to a fifth embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the film comprises a polymer as a continuous phase and dispersed uniformly therein an amorphous high polymer with a higher glass transition temperature than the glass transition temperature of the continuous phase and/or a crystalline high polymer with a melting point higher than the glass transition phase of the continuous phase and inorganic opacifying pigment as particles all having a refractive index of at least 2.0 in a total concentration of between 0.5 and 5% by weight of said film.

According to a sixth embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the film is a biaxially stretched film.

According to a seventh embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the film comprises a polyolefin as continuous phase.

According to an eighth embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the film comprises polypropylene as continuous phase.

According to a ninth embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the film comprises a linear polyester as continuous phase.

According to a tenth embodiment of the process for obtaining a permanent transparent pattern permanent transparent pattern, according to the present invention, in the continuous phase linear polyester matrix is uniformly dispersed from 7 to 35% by weight of the film of a high polymer, the high polymer being an amorphous high polymer having a higher glass transition point than the glass transition temperature of the linear polyester and/or a crystalline high polymer having a higher melting point than the glass transition temperature of the linear polyester.

According to an eleventh embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the concentration of inorganic opacifying pigment is ≧1% by weight.

According to a twelfth embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the heat is applied by a heated or hot stamp, a thermal head, a heated or hot bar or a laser. The heating can be carried out from one or both sides of the film. The transparentization realized upon obtaining a permanent transparent pattern, according to the present invention, increases with decreasing film thickness, with thicknesses of 100 μm or less being preferred. Optical density changes of at least 0.4 can be readily realized or up to 40% without significant changes in film thickness. Moreover, the transparentization effect realized by the process for obtaining a permanent transparent pattern, according to the present invention, results from a combination of heat supplied by a heat source, the pressure between the heat source and the film and the time the heat source is applied. The heat has to be applied for at least 1 ms either continuously or non-continuously. Heating with a thermal head can be with a single heat pulse, but multiple short heating pulses are preferred to avoid overheating of the heating elements. When a thermal head is used a foil can be used between the thermal head and the non-transparent microvoided axially stretched self-supporting polymeric film during the heating process e.g. a 6 μm thick PET-film can be interposed between the non-transparent microvoided film and the thermal head to prevent possible contamination of the thermal head. Thermal head printers, such as the DRYSTAR-printers supplied by AGFA-GEVAERT N.V., can be used to produce the permanent transparent pattern of the present invention e.g. as personalized watermarks.

This transparentization effect is accompanied by a relief pattern, which can be detected by touch i.e. in a tactile manner. This relief pattern is more pronounced the higher the temperature of the heat source, this embossing effect increasing with temperature between 110° C. and 190° C. The tactile relief obtained by applying a hot stamp to a non-transparent microvoided axially stretched self-supporting polymeric film is much more pronounced than that obtained using a thermal head.

The degree of transparency realized depends upon the stamp/thermal head printing conditions: time, temperature and pressure. The thermofixation history of the material is also important. The heated-induced transparentization of the non-transparent microvoided axially stretched self-supporting polymeric film can be carried out before or after the optional application of a layer, such as an ink-jet receiving layer and before or after transparentization. The relative positioning of the transparentized areas and transparency in the support can be of value as an additional security measure.

According to a thirteenth embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the non-transparent microvoided axially stretched self-supporting polymeric film further comprises a whitening agent, preferably in a concentration of ≦0.5% by weight of the film.

According to a fourteenth embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, the heat is applied non-continuously.

According to a fifteenth embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, a transparent overprintable layer is provided on the film prior to the image-wise application of heat.

According to a sixteenth embodiment of the process for obtaining a permanent transparent pattern, according to the present invention, a transparent overprintable layer is provided on the film after the image-wise application of heat.

INDUSTRIAL APPLICATION

Permanent transparent patterns in non-transparent microvoided axially stretched self-supporting films, according to the present invention, can be used in security and anti-counterfeiting applications e.g. in tickets, labels, tags, an ID-card, a bank card, a legal document, banknotes and packaging and can also be integrated into packaging.

The invention is illustrated hereinafter by way of comparative examples and invention examples. The percentages and ratios given in these examples are by weight unless otherwise indicated.

Subbing layer Nr. 01 on the emulsion side of the support:

copolymer of 88% vinylidene chloride, 10% methyl 79.1 mg/m² acrylate and 2% itaconic acid Kieselsol ® 100F, a colloidal silica from BAYER 18.6 mg/m² Mersolat ® H, a surfactant from BAYER  0.4 mg/m² Ultravon ® W, a surfactant from CIBA-GEIGY  1.9 mg/m² Ingredients used in the EXAMPLES:

Polyester:

MFI 270° C./ Inherent PET- 1.20 kg viscosity** T_(g) nr [cm³/10 min] [η] [dl/g] [° C.] 01 T03* polyethylene terephthalate 34.8 0.60 80.5 02 T04* polyethylene terephthalate 34.8 0.60 80.5 03 WP75 # polyester of 98.5 mol % 0.77 80 terephthalate, 1.5 mol % isophthalate and 100 mol % ethylene units 04 DP9990 # polyester of 90 mol % 0.60 terephthalate, 10 mol % isophthalate and 100 mol % ethylene units 05 DP9970 # polyester of 70 mol % terephthalate, 30 mol % isophthalate and 100 mol % ethylene units 06 RADICRON polyester of 100 mol % 1480 # terephthalate, 73 mol % ethylene and 27 mol % neopentylene units *AGFA-GEVAERT N.V. # La Seda **inherent viscosity was determined in a 0.5 g/dL solution of 60 wt % phenol and 40 wt % ortho-dichlorobenzene at 25° C. in an Ubbelohde viscometer

Styrene-Acrylonitrile Copolymers:

MFI at 270° C./ SAN- Wt % Wt % 1.20 kg T_(g) nr acrylonitrile styrene [mL/10 min] Mn Mw [° C.] 01 TYRIL 905* 20 80 7.1 105.2 02 TYRIL 867E* 25 75 5.8 106.5 03 SAN 140* 27.5 72.5 53.2 47,640 99,820 108.8 04 LURAN 368R# 28 72 3.9 107.3 05 TYRIL 790* 29 71 12.1 106.3 06 SAN 124* 28.5 71.5 37.9 53,940 109,350 108.1 07 LURAN 388S# 33 67 3.6 108.7 *DOW CHEMICAL #BASF MFI = Melt Flow Index

-   MAGNUM 8391: an ABS-resin with a Vicat softening temperature of 95°     C., from DOW CHEMICAL -   TPX® DX820: a high rigidity poly(4-methylpentene) from MITSUI     CHEMICAL -   BARIUM SULPHATE: NEOBRK/renol white, a masterbatch from CLARIANT     GmbH containing 50% by weight barium sulphate and 50 wt % polyester -   TITANIUM DIOXIDE: Renol-white/PTX 506, a masterbatch from CLARIANT     GmbH containing 65% by weight TiO₂ and 35 wt % polyester

EXAMPLES 1 to 58

Extrudates 1 to 4 were produced by mixing the respective parts of PET 01, PET 03, of the particular SAN used, BaSO₄ and UVITEX OB-one given in Table 1, drying the resulting mixture at 150° C. for 4 hours under vacuum (<100 mbar), melting them in a PET-extruder and finally extruding them through a sheet die and cooling the resulting extrudates.

TABLE 1 UVITEX PET/ Extrudate PET01 PET03 SAN06 BaSO₄ OB-one SAN wt. nr [wt %] [wt %] [wt %] [wt %] [ppm] ratio 1 42.5 42.5 15 0 — 5.67 2 39.5 39.5 19 2 150 4.16 3 39.5 39.5 21 0 — 3.76 4 38 38 24 0 — 3.17

Extrudates 1 to 4 were axially stretched longitudinally with an INSTRON apparatus in which the extrudates are heated in an oven mounted on the apparatus under the conditions given in Table 2 to yield the axially stretched films of EXAMPLES 1 to 23, EXAMPLES 24 to 35, EXAMPLES 36 to 46 and EXAMPLES 47 to 58 respectively.

TABLE 2 Extrudate Stretch EXAM- used tempera- Stretch Stretch PLE in film Stretch ture tension speed Optical nr production ratio [° C.] [N/mm²] [%/min] density 1 1 1.8 85 2.9 1500 0.33 2 1 2.4 85 3.5 1500 0.53 3 1 2.3 85 3.7 1500 0.49 4 1 2.6 85 4.9 1500 0.47 5 1 2.8 85 5.6 1500 0.47 6 1 2.9 85 5.7 1500 0.47 7 1 1.3 85 2.4 750 0.17 8 1 2.5 85 4.8 1100 0.49 9 1 2.9 85 5.4 750 0.51 10 1 2.2 85 2.8 750 0.49 11 1 3.9 93 3.6 750 0.31 12 1 1.6 93 1.7 1500 0.17 13 1 3.2 93 3.4 1500 0.37 14 1 3.1 93 3.2 1500 0.36 15 1 2.9 93 3.0 1500 0.35 16 1 2.9 100 1.3 1500 0.19 17 1 5.2 100 1.9 1130 0.24 18 1 4.4 100 1.6 1130 0.22 19 1 4.2 100 1.6 1130 0.21 20 1 1.5 100 1.1 750 0.13 21 1 4.2 105 0.9 1130 0.16 22 1 4.0 105 0.8 1130 0.16 23 1 1.5 105 0.7 750 0.10 24 2 2.9 85 6.4 750 0.68 25 2 2.1 85 3.3 750 0.56 26 2 3.9 93 4.9 750 0.53 27 2 1.6 93 2.1 1500 0.37 28 2 3.6 93 5.9 1500 0.54 29 2 3.8 100 3.1 1500 0.47 30 2 4.0 100 3.1 1500 0.45 31 2 1.5 100 1.2 750 0.24 32 2 3.0 100 2.0 1500 0.41 33 2 2.8 100 1.9 1500 0.41 34 2 1.5 105 0.7 750 0.16 35 2 2.8 105 1.1 1500 0.31 36 3 2.8 85 6.9 1500 0.58 37 3 3.0 85 8.9 1500 0.60 38 3 3.4 93 6.5 1500 0.46 39 3 1.5 93 1.8 750 0.20 40 3 3.0 93 4.8 1130 0.46 41 3 2.9 93 4.4 1130 0.43 42 3 4.0 100 1.6 750 0.24 43 3 1.7 100 1.5 1500 0.22 44 3 1.5 100 1.5 1500 0.16 45 3 4.0 105 0.8 750 0.18 46 3 1.5 105 1.0 1500 0.14 47 4 2.7 85 6.9 750 0.62 48 4 2.0 85 4.6 750 0.69 49 4 3.6 93 5.2 750 0.45 50 4 1.8 93 2.7 1500 0.48 51 4 1.6 93 2.4 1500 0.38 52 4 3.4 93 6.0 1130 0.49 53 4 4.0 100 3.0 1130 0.34 54 4 1.5 100 1.5 1130 0.24 55 4 3.0 100 2.8 1500 0.36 56 4 2.9 100 2.8 1500 0.38 57 4 1.6 105 1.1 1130 0.15 58 4 2.8 105 1.3 1500 0.26 These experiments show that the opacity increased with stretching and with decreasing stretching temperature down to 85° C., just above the T_(g) of the polyethylene terephthalate continuous phase. Furthermore, these experiments show that the optical density increased by about 0.15 upon incorporation of 3% by weight of barium sulphate. Moreover, these experiments also show that the optical density also increased with the stretching tension. Two minutes heating time was sufficient to give a self-consistent, i.e. homogeneous, group of measurements. The following equation was derived from the data of Table 2 by a partial least squares regression using Unscrambler software with quadratic effects or interactions not being found to be relevant:

Optical  density = 1.273362 − 0.0270 × PET/SAN  wt  ratio + 0.0496 × [BaSO₄ − concentration  in  film  in  wt  %] + 0.0394 × [stretching  tension  in  N/mm²]

The stretching speed was not found to have a significant influence upon the optical density observed, although the results appear to show that it has a minor effect as does the stretching tension. Particularly high opacities appeared to be obtained for stretching tensions greater than 4 N/mm².

In films with a dispersion of styrene-acrylonitrile copolymer optionally together with barium sulphate in a continuous phase of polyethylene terephthalate the opacity is almost exclusively due to micropores in the film, because the differences in refractive index between styrene-acrylonitrile copolymers with a refractive index of 1.56 to 1.57 and polyethylene terephthalate with a refractive index of 1.58 to 1.64 on the one hand and between barium sulphate with a refractive index of 1.63 and polyethylene terephthalate with a refractive index of 1.58 to 1.64 on the other are negligible.

EXAMPLES 59 to 78

The PET-types and SAN-types used for producing the extrudate used in producing of the films of EXAMPLES 59 to 78 are given in Table 3. The PET, SAN, BaSO₄ and UVITEX OB-one in the weight percentages given in Table 3 were mixed and then dried at 150° C. for 4 hours under vacuum (<100 mbar), the mixtures then melted in a PET-extruder and extruded through a sheet die and cooled to produce the extrudates 1, 2 and 5 to 22.

TABLE 3 PET/ SAN Extrudate PET01 PET03 SAN SAN BaSO₄ OB-one wt nr [wt %] [wt %] type [wt %] [wt %] [ppm] ratio 5 85 — 03 15 0 — 5.67 6 85 — 06 15 0 — 5.67 1 42.5 42.5 06 15 0 — 5.67 7 82 — 06 18 0 — 4.56 8 41 41   06 18 0 — 4.56 9 79 — 06 21 0 — 3.76 10 39.5 39.5 06 21 0 150 3.76 11 39.5 39.5 06 21 0 150 3.76 12 76 — 06 24 0 — 3.17 13 39.5 39.5 06 20 1 150 3.95 14 40.5 40.5 06 17 2 150 4.76 15 39.5 39.5 06 19 2 150 4.16 2 39.5 39.5 06 19 2 150 4.16 16 39.5 39.5 06 19 2 150 4.16 17 39.5 39.5 06 19 2 — 4.16 18 39.5 39.5 06 19 2 150 4.16 19 39.5 39.5 06 19 2 150 4.16 20 39.5 39.5 06 19 2 150 4.16 21 39.5 39.5 06 19 2 150 4.16 22 39.5 39.5 06 18 3 150 4.39 Extrudates 1, 2 and 5 to 22 were then stretched as given in Tables 4 and 5 for the non-barium sulphate-containing substantially opaque films of INVENTION EXAMPLES 59 to 67 and for the barium sulphate-containing substantially opaque films of INVENTION EXAMPLES 68 to 78 respectively and finally thermally fixated at 175° C. for 2 minutes.

TABLE 4 Longitudinal Transversal stretch stretch OD after EXAMPLE Extrudate SAN force* temperature Thickness thermal nr nr [wt %] ratio [N/mm²] ratio [° C.] [μm] fixation 59 5 15 3.3 5.0 3.3 112 — 0.60 60 6 15 3.6 8.39 3.0 156 145 0.878 61 1 15 3.3 7.87 3.5 112 150 0.85 62 7 18 3.6 8.39 3.3 140 130 0.92 63 8 18 3.6 7.89 3.3 145 161 0.91 64 9 21 3.6 7.89 3.3 145 130 0.90 65 10 21 3.6 8.03 3.3 160 120 0.92 66 11 21 3.8 8.33 3.3 163 100 0.93 67 12 24 3.6 8.11 3.3 165 149 0.95 *the lower the force temperature the higher the stretch tension

TABLE 5 Longitudinal Transversal stretch stretch OD after EXAMPLE Extrudate SAN BaSO₄ tension* temperature Thickness thermal nr nr [wt %] [wt %] ratio [N/mm²] ratio [° C.] [μm] fixation 68 12 20 1 3.6 9.21 3.3 166 100 1.02 69 13 17 2 3.8 8.0 3.3 140 90 0.92 70 14 19 2 3.6 8.0 3.3 160 130 1.06 71 2 19 2 3.6 8.33 3.3 164 100 0.98 72 15 19 2 3.6 8.0 3.3 145 105 1.00 73 16 19 2 3.8 8.0 3.3 170 100 1.10 74 17 19 2 3.8 8.0 3.3 170 95 1.09 75 18 19 2 3.8 8.0 3.3 170 125 1.22 76 19 19 2 3.8 8.0 3.3 125 75 1.02 77 20 19 2 3.85 8.0 3.3 125 0.96 78 21 18 3 3.6 8.32 3.3 163 98 0.99 *the lower the stretch temperature the higher the stretch tension

In films with a dispersion of styrene-acrylonitrile copolymer in a continuous phase of polyethylene terephthalate the opacity is almost exclusively due to micropores in the film, because the difference in refractive index between styrene-acrylonitrile copolymers with a refractive index of 1.56 to 1.57 and polyethylene terephthalate with a refractive index of 1.58 to 1.64 is negligible. Moreover, the incorporation of barium sulphate with a refractive index of 1.63 also provides a negligible contribution to the opacity for the same reasons. SEM-evaluation of the biaxially stretched and thermofixated film showed that the dispersed SAN 06 had a particle size of ca. 1.5 μm and that the barium sulphate particles in the films of INVENTION EXAMPLES 68 to 78 had a particle size of ca. 0.5 μm.

Up to a SAN-concentration of 21 wt % the optical density appears to increase with increasing SAN-concentration. Above a SAN-concentration of 21 wt %, the SAN-concentration had no significant effect on the optical density of the biaxially stretched film. Incorporation of barium sulphate brought about a further significant increase in the optical density of the films produced.

The changes in optical density and shrinkage of the films of INVENTION EXAMPLES 65, 67, 68 and 70 after 30 minutes at 100, 115 and 130° C. were then determined and the results are given in Tables 6 and 7 respectively below.

The results in Tables 6 and 7 demonstrate the dimensional stability of the non-transparent microvoided axially stretched self-supporting polymeric films comprising ≦3% by weight of inorganic opacifying pigment each with a refractive index of less than 2.0 subjected to the image-wise heating process of the present invention to provide a permanent transparent pattern, according to the present invention.

TABLE 6 ΔOD after 2 min Subsequent to thermal fixation EXAMPLE BaSO₄ at 150° C. thermal ΔOD after 30 min ΔOD after 30 min ΔOD after 30 min nr [wt %] fixation at 100° C. at 115° C. at 130° C. 66 0 −0.01 −0.03 −0.02 −0.01 68 1 −0.04 −0.07 −0.08 −0.09 71 2 0.00 −0.03 −0.04 −0.07 78 3 −0.01 −0.05 −0.07 −0.09

TABLE 7 After 2 min at 150° C. thermal fixation % Shrinkage % Shrinkage % Shrinkage EXAMPLE BaSO₄ after 30 min after 30 min after 30 min nr [wt %] at 100° C. at 115° C. at 130° C. 66 0 1.7 4.2 6.4 68 1 2.0 4.7 6.9 71 2 1.6 3.9 5.9 78 3 1.7 4.3 6.1

INVENTION EXAMPLE 79

The film of INVENTION EXAMPLE 72 was mounted in an Instron 4411 apparatus and was heated at temperatures between 138 and 200° C. for 5 seconds with a soldering iron in the upper clamp making contact with the film at a pressure of 0.5 N/mm². The optical densities of the film after the test were measured in transmission with a MacBeth TR924 densitometer with a visible filter. The results are summarized in Table 8 below.

TABLE 8 Temperature [° C.] Optical density, OD ΔOD % reduction in OD before heating 1.12 138 1.00 0.12 10.7 150 0.91 0.31 27.7 175 0.61 0.51 45.5 200 0.42 0.70 62.5 In other experiments the thermofixated stretched film was heated at a temperature of 175° C. for 5 seconds at different pressures between 0.1 N/mm² to 1.50 N/mm² in the Instron apparatus with the results shown in Table 9 below.

TABEL 9 Pressure [N/mm²] Optical density ΔOD % reduction in OD before heating 1.12 0.01 1.06 0.06 5.4 0.10 0.92 0.20 17.9 0.50 0.61 0.51 45.5 1.00 0.51 0.61 54.5 1.50 0.40 0.72 64.3

In further experiments the thermofixated stretched film was heated at a temperature of 175° C. and a pressure of 0.5 N/mm² in the Instron apparatus for different times between 2 and 300 seconds with the results shown in Table 10 below.

TABEL 10 Heating time [s] Optical density ΔOD % reduction in OD before heating 1.12  2 0.68 0.44 39.3  5 0.61 0.51 45.5 10 0.56 0.56 50 30 0.51 0.61 54.5 60 0.45 0.67 59.8 300  0.41 0.71 63.4 These experiments demonstrate that the transparentization effect is due to a combination of the temperature of the transparentization entity and the pressure with which it is applied and time for which it is applied. Considerable changes in optical density can be realized at accessible temperatures and pressures in relatively short times.

INVENTION EXAMPLE 80

Transparentization tests were carried out on the film of INVENTION EXAMPLE 66 as described in INVENTION EXAMPLE 79. The temperature was varied with a contact pressure of 0.5 N/mm² and a contact time of 5 seconds as described for INVENTION EXAMPLE 79 with the results given in Table 11.

TABLE 11 Temperature [° C.] Optical density, OD ΔOD % reduction in OD before heating 0.93 138 0.75 0.18 19.4 150 0.73 0.20 21.5 175 0.52 0.41 44.1 200 0.31 0.62 66.7 These experiments show that the presence of barium sulphate is not necessary to realize transparentization.

INVENTION EXAMPLE 81

Hostaphan™ WO195.0D027B, a non-transparent PET pigmented with 17% by weight of BaSO₄ from Mitsubishi Paper Mills was subjected to the transparentization test described in INVENTION EXAMPLE 79. In films with barium sulphate in a continuous phase of polyethylene terephthalate the opacity is almost exclusively due to micropores in the film, because the difference in refractive index between barium sulphate with a refractive index of 1.63 and polyethylene terephthalate with a refractive index of 1.58 to 1.64 is negligible.

The temperature was varied with a contact pressure of 0.5 N/mm² and a contact time of 5 seconds as described for INVENTION EXAMPLE 79 with the results given in Table 12.

Significant transparentization was observed at 200° C. with a change in optical density of 0.24. This shows that addition of a styrene-acrylonitrile copolymer has a significant effect upon the temperature at which transparentization is first observed and also upon the degree of transparentization observed.

TABLE 12 Temperature [° C.] Optical density, OD ΔOD % reduction in OD before heating 1.52 138 1.52 0.0 0 150 1.51 0.01 0.7 175 1.47 0.05 3.3 200 1.24 0.28 18.4

INVENTION EXAMPLE 82

A 8 inch (203.2 mm) by 10 inch (254 mm) piece of the film of INVENTION EXAMPLE 65 (120 μm thick and with an optical density of 0.92) was fed into a standard DRYSTAR DS5500 printer from AGFA-GEVAERT N.V. with a Toshiba thermal head and a rectangular area printed at a line time of 4.3 ms with the maximum power of 49.5 mW. The printed area had an optical density of 0.80 as measured with a MacBeth TR924 densitometer with a visual filter. The low reduction in optical density is probably due to a too low pressure between the sheet and the thermal head due to the DS5500 printer being designed for film ca. 200 μm thick with a 175 μm thick support rather than the 100 μm thick film used in the experiment.

This experiment was then repeated with a second piece of this film 8 inch (203.2 mm) by 10 inch (254 mm) in size mounted with double-sided tape on a sheet of DS2 thermographic film from AGFA-GEVAERT and again fed into the DRYSTAR DS 5500 printer using the same print conditions except that the maximum power was 42.5 mW rather than 49.5 mW. The printed area had an optical density of 0.64 as measured with a MacBeth TR924 densitometer with a visual filter. The change in optical density of 0.28 observed is sufficient to demonstrate that conventional thermal head printers can be used to provide a permanent transparent pattern in non-transparent microvoided axially stretched self-supporting polymeric films comprising ≦3° by weight of inorganic opacifying pigment each with a refractive index of less than 2.0, according to the present invention. These transparency changes were associated with a pronounced relief pattern, which was clearly detectable by touch.

INVENTION EXAMPLE 83

YUPO® FPG 200, a synthetic paper from YUPO CORPORATION, is a multi-layered biaxially oriented polypropylene in which the inorganic opacifying pigment calcium carbonate with a refractive index of less than 2.0 is dispersed. It has opacity and whiteness as a result of microvoids resulting from extrusion and biaxial stretching during its manufacturing process. YUPO® synthetic paper was subjected to the transparentization test described in INVENTION EXAMPLE 79. The temperature was varied with a contact pressure of 0.5 N/mm and a contact time of 5 seconds as described for INVENTION EXAMPLE 79 with the results given in Table 13.

Significant transparentization as shown by a change in optical density of 0.35 was observed at 110° C., which clearly was not associated with melting since the film thickness did not change significantly between 110 and 135° C. This effect was accompanied by a change in thickness i.e. a tactile effect.

TABLE 13 Temperature Optical density, % reduction film thickness [° C.] OD ΔOD in OD [μm] before heating 1.25 — 171 110 0.86, 0.95 0.35 28 153, 160 135 0.97, 0.94 0.29 23 162, 159

INVENTION EXAMPLES 84

The 85 parts of polyethylene terephtalate and 15 parts of isotactic polypropylene type Appryl® 3030 BN from ATOCHEM, with a melting temperature of 162.8° C. (10° C./min), a density of 0.905 g/mL and a melt flow index at 230° C./2.16 kg of 3 g/10 min, were mixed and then dried at 150° C. for 4 hours under vacuum (<100 mbar), the mixture was then melted in a PET-extruder, extruded through a sheet die and then after cooling was stretched longitudinally to a stretch ratio of 3.3 at a stretching tension of 3.3 N/mm and then transversally to a stretch ratio of 3.3 at 100° C.

The temperature was varied with a contact pressure of 0.5 N/mm² and a contact time of 5 seconds as described for INVENTION EXAMPLE 77 with the results given in Table 14.

TABLE 14 Temperature [° C.] Optical density, OD ΔOD % reduction in OD before heating 0.93 110 0.92 0.01 1 135 0.94 — — 150 0.91 0.02 2.1 175 0.83 0.10 10.8 200 0.66 0.27 29.0 Significant transparentization was observed at 200° C.

INVENTION EXAMPLE 85

Transparentization tests were carried out on the film of INVENTION EXAMPLE 77 as described in INVENTION EXAMPLE 79. The transparentization was determined at various temperatures between 120 and 190° C. at a contact pressure of 0.5 N/mm² and a contact time of 5 seconds as described for INVENTION EXAMPLE 79 with the results given in Table 15.

TABLE 15 Optical % reduction Film thickness Temperature [° C.] density, OD ΔOD in OD [μm] before heating 0.96 73 120 0.67 0.29 30.2 73 130 0.57 0.39 40.6 72 150 0.57 0.39 40.6 72 170 0.34 0.62 64.6 69 190 0.29 0.67 69.8 66

INVENTION EXAMPLES 86 to 90 and COMPARATIVE EXAMPLES 1 to 3

The PET-types and SAN-types used for producing the extrudates used in producing of the films of EXAMPLES 86 to 90 and COMPARATIVE EXAMPLES 1 to 3 are given in Table 16. The PET, SAN, titanium dioxide and UVITEX OB-one in the weight percentages given in Table 16 were mixed and then dried at 150° C. for 4 hours under vacuum (<100 mbar), the mixtures then melted in a PET-extruder and extruded through a sheet die and cooled to produce INVENTION EXTRUDATES 22 to 26 and COMPARATIVE EXTRUDATES 1 to 3.

TABLE 16 PET01 PET03 PET04 SAN SAN Rutile OB-one PET/SAN [wt %] [wt %] [wt %] type [wt %] [wt %] [ppm] wt ratio Invention Extrudate nr 22 39.5 39.5 — 06 19 2 — 4.16 23 39.5 39.5 — 06 19 2 150 4.16 24 39.5 — 39.5 06 19 2 — 4.16 25 39.5 39.5 — 06 19 2 — 4.16 26 39 39   — 06 18 4 — 4.33 Comparative Extrudate nr  1 98 — — — — 2 150 —  2 47 — 47   — — 6 — —  3 44 — 44   — — 12 — — INVENTION EXTRUDATES 22 to 26 and COMPARATIVE EXTRUDATES 1 to 3 were then stretched and finally thermally fixated at 175° C. for 1 minute as given in Tables 2 and 3 for the substantially opaque films of INVENTION EXAMPLES 86 to 90 and those of COMPARATIVE EXAMPLES 1 to 3 respectively.

The optical densities of the films of INVENTION EXAMPLES 86 to 90 and the films of COMPARATIVE EXAMPLES 1 to 3 were measured in transmission with a MACBETH TR924 densitometer with a visible filter and the results given in Tables 17 and 18 for the films of INVENTION EXAMPLES 86 to 90 and those of COMPARATIVE EXAMPLES 1 to 3 respectively.

TABLE 17 Invention Example nr 86 87 88 89 90 Invention Extrudate nr 23 24 25 26 27 SAN [wt %] 19 19 19 19 17 Titanium dioxide [wt %] 2.0 2.0 2.0 2.0 4.0 Longitudinal stretch ratio 3.6 3.3 3.8 3.8 3.8 Longitudinal stretch 8.0 6.0 8.5 8.35 8.0 tension* [N/mm²] Transversal stretch ratio 3.8 3.3 3.3 3.3 3.3 Transversal stretch 125 135 135 135 125 temperature [° C.] Thickness [μm] 120 106 102 Optical density after 1.24 1.15 1.17 1.19 1.41 thermal fixation *the lower the stretch temperature the higher the stretch tension

TABLE 18 Comparative Example nr 1 2 3 Comparative Extrudate nr 1 2 3 Titanium dioxide [wt %] 2.0 6.0 12.0 Longitudinal stretch ratio 3.3 3.3 3.3 Longitudinal stretch tension* [N/mm²] 6.0 5.0 5.0 Transversal stretch ratio 3.3 3.3 3.3 Transversal stretch temperature [° C.] 135 135 135 Thickness [μm] 140 135 Optical density after thermal fixation 0.45 0.90 1.12 *the lower the stretch temperature the higher the stretch tension

The contribution to the substantial opacity of the films of INVENTION EXAMPLES 86 to 90 from the dispersion of styrene-acrylonitrile copolymer in a continuous phase of polyethylene terephthalate is almost exclusively due to micropores in the film, because the difference in refractive index between styrene-acrylonitrile copolymers with a refractive index of 1.56 to 1.57 and polyethylene terephthalate with a refractive index of 1.58 to 1.64 is negligible. However, the contribution to the substantial opacity of the films of INVENTION EXAMPLES 86 to 90 from the dispersion of titanium dioxide in a continuous phase of polyethylene terephthalate is almost exclusively due to the refractive index difference between titanium dioxide with a refractive index of 2.76 and that of polyethylene terephthalate with a refractive index of 1.58 to 1.64.

SEM-evaluation of the biaxially stretched and thermofixated film showed that the dispersed SAN 06 in the films of INVENTION EXAMPLES 86 to 90 had a particle size of ca. 1.5 μm and that the titanium dioxide particles in the films of INVENTION EXAMPLES 86 to 90 had a particle size of ca. 0.2 μm.

The films of INVENTION EXAMPLES 87, 88 and 90 and COMPARATIVE EXAMPLES 1 to 3 were each mounted in an Instron 4411 apparatus and were heated at various temperatures between 120 and 190° C. for 5 seconds with a soldering iron in the upper clamp making contact with the film at a pressure of 0.5 N/mm². The optical densities (OD) of the film after the tests were measured in transmission with a MacBeth TR924 densitometer with a visible filter and the film thicknesses were also measured. The results are summarized below in Tables 19 and 20 respectively.

TABLE 19 OD OD after heating for 5 s at a ΔOD % before pressure of 0.5 N/mm² at at decrease heating 120° C. 130° C. 150° C. 170° C. 190° C. 150° C.  in OD Film of Invention Example nr 87 1.15 0.92 0.84 0.85 0.60 0.61 0.30 26.1 88 1.15 0.94 0.78 0.75 0.59 0.53 0.40 34.8 90 1.41 1.26 1.16 1.13 0.99 0.92 0.28 19.9 Film of Comparative Example nr  1 0.45 0.47 0.46 0.46 0.47 0.45 −0.01 −0.01  2 0.90 0.90 0.91 0.89 0.88 0.85 0.01 0.01  3 1.12 1.14 1.14 1.11 1.11 1.08 0.01 0.01

TABLE 20 Film thickness Film thickness after heating for 5 s before at a pressure of 0.5 N/mm² at heating 120° C. 130° C. 150° C. 170° C. 190° C. Film of Invention Example nr 87 102 103 102 98 89 98 88 116 113 109 111 100 94 90 105 102 102 99 92 89 Film of Comparative Example nr  1 93 92 91 93 92 85  2 138 139 142 137 132 115  3 137 136 135 139 131 119

Significant transparentization was observed upon heating the films of INVENTION EXAMPLES 87, 88 and 90 without substantial change in film thickness, whereas within experimental error no transparentization was observed upon heating the films of COMPARATIVE EXAMPLES 1 to 3.

This shows that in the presence of titanium dioxide transparentization is observed in non-transparent microvoided axially stretched self-supporting polymeric film comprising a polymer as a continuous phase and dispersed uniformly therein an amorphous high polymer with a higher glass transition temperature than the glass transition temperature of the continuous phase, although there is no transparentization of the contribution to the non-transparency due to the presence of titanium dioxide.

COMPARATIVE EXAMPLE 4

The ca. 1100 μm thick extrudate of COMPARATIVE EXAMPLE 4 with a composition of 1.7% by weight of titanium dioxide and 98.3% by weight of GP1 was produced as described for EXAMPLES 1 to 58 and was stretched in the length direction as described in EXAMPLES 1 to 58 under the conditions given in Table 18.

TABLE 18 Comparative Stretch Stretch force Thickness OD OD Example nr. ratio [N/mm²] [μm] (TR924) [X-rite] 4/LS1 3.35 9 330 1.14 0.87 4/LS2 3.35 7 1.04 0.81 4/LS3 3.35 5 1.02 0.78 Transversal stretching was then performed as described in EXAMPLES 1 to 58 on the length-stretched films with a stretch time of 30 s and stretching speed of 1000%/min under the conditions given in Table 19. The measured thickness and optical density measured with a MacBeth TR924 densitometer in transmission mode with a visible filter are also given in Table 19.

TABLE 19 Comparative Transversal stretch Thickness OD OD Example nr. ratio temperature [° C.] [μm] (TR924) [X-rite] 4/LS1/BS1 3.3 135 137 1.34, 1.33 1.05 4/LS2/BS1 3.3 135 140, 137 0.53 0.99 The film of COMPARATIVE EXAMPLE 4/LS1/BS1 was then clamped in an Instron 4411 apparatus and subjected to heating with a soldering iron at 150° C. for 5 s. The effect upon the film thickness and optical density is given in Table 20.

TABLE 20 OD (TR924) Film thickness [μm] before heating 1.33 137 after heating at 150° C. for 5 s 1.25 130

These changes in optical density and film thickness are minimal and demonstrate that no void-forming occurs in polyester compositions containing 2% by weight of titanium dioxide.

COMPARATIVE EXAMPLE 5

The 1083 μm thick extrudate of COMPARATIVE EXAMPLE 5 with a composition of 2% by weight of titanium dioxide, 100 ppm UVITEX OB-one and 98% by weight of TO4 was produced as described for EXAMPLES 1 to 58 and had an optical density measured with a MacBeth TR924 densitometer in transmission mode with a visible filter of 1.35. The extrudate was stretched in the length direction as described in EXAMPLES 1 to 58 under the conditions given in Table 20.

TABLE 20 Comparative Longitudinal stretch Thickness OD OD Example nr. ratio force [N/mm²] [μm] (TR924) [X-rite] 5/LS1 3.3 6 323 0.805 0.55 5/LS2 3.3 4 328 0.84 — Transversal stretching was then performed on the length-stretched films with a stretch time of 30 s and stretching speed of 1000%/min as described in EXAMPLES 1 to 58 under the conditions given in Table 21. The measured thickness and measured optical density with the MacBeth TR924 densitometer in transmission mode with a visible filter are also given in Table 21.

Since there is no contribution to the optical density from void-forming upon biaxial stretching for the composition of COMPARATIVE EXAMPLE 5 as can be seen from COMPARATIVE EXAMPLE 1 to 4, the dependence of optical density upon film thickness can be used to provide a baseline with which to assess the contribution of void-forming to the optical density for those compositions based upon aromatic polyesters with 2% by weight of the same titanium dioxide pigment which form voids upon biaxial stretching.

TABLE 21 Comparative Transversal stretch Thickness OD OD Example nr. ratio temperature [° C.] [μm] (TR924) [X-rite] 5/LS1/BS1 3.3 135 120 0.47 0.30 5/LS2/BS1 3.3 135 124 0.53 0.33

The Beer-Lambert relationship does not hold for pigmented films with light-scattering pigments such as titanium dioxide. If the film thickness is smaller than the average free path-length of the scattered light, light will escape after scattering otherwise the light does not escape and in fact interferes with further scattered light providing for a quasi-exponential dependence of optical density upon film thickness. The situation is too complex to be able to be described theoretically and hence the only possible approach is to measure the actual optical density observed at particular film thicknesses. The above-mentioned optical density appear to a fair approximation to bee linearly dependent upon the logarithm of the film thickness in the layer thickness range 1084 to 120 μm giving the following relationship:

OD=0.891 log [thickness in μm]−1.3727

This relationship provides the optical density attributable to a 2% by weight concentration of the titanium dioxide pigment used as a function of film thickness.

INVENTION EXAMPLES 91 to 101

The ca. 1100 μm thick extrudates of EXAMPLES 91 to 101 all with 2% by weight of titanium dioxide and 15% by weight of SAN 06 were produced by mixing the ingredients in Table 22 in the proportions given in Table 22 and then drying the mixture at 150° C. for 4 hours under vacuum (<100 mbar) before melting in a PET-extruder, extrusion through a sheet die and cooling to produce the extrudates of EXAMPLES 91 to 101 having a density of ca. 1.3 g/mL as summarized in Table 22.

TABLE 22 Exam- TO4 UVITEX ple [wt PET04 SAN SAN OB-one TiO₂ Density nr. %] [wt %] type [wt %] [ppm] [wt %] [g/mL] 91 83 0 06 15 — 2.0 1.294 92 58 25 06 15 — 2.0 1.289 93 41.5 41.5 06 15 100 2.0 1.284 94 33.3 49.7 06 15 100 2.0 95 32.3 50.7 06 15 100 2.0 96 32.3 50.7 06 15 100 2.0 97 26.29 56.71 06 15 100 2.0 98 25.25 57.75 06 15 100 2.0 99 25 58 06 15 100 2.0 1.304 100 24.3 58.7 06 15 100 2.0 101 — 83 06 15 — 2.0 1.299 Longitudinal stretching was carried out for each extrudate as described in EXAMPLES 1 to 58 under the conditions given in Table 23. The expected thickness is the thickness based on the extrudate thickness and longitudinal as observed for non-voided films.

TABLE 23 Longitudinal stretch temper- Example ature force Density Thickness [μm] nr. [° C.] ratio [N/mm²] [g/mL] measured expected  91/LS1 3.85 8 1.290 320 286  92/LS1 3.85 8 1.264 325 286  92/LS2 3.65 8 323 301  93/LS1 3.85 8 1.251 318 286  94/LS1 101 3.3 8 1.216 350 333  94/LS2 116 3.3 8 1.283 330 333  95/LS1 3.3 8.6 365 333  96/LS1 120 3.8 8 300 290  96/LS2 96 3.6 8 335 305  96/LS3 85 3.45 8 350 319  97/LS1 92 3.3 8 1.229 360 333  98/LS1 95 3.3 8 1.242 330 333  99/LS1 3.85 8 1.217 330 286 100/LS1 94 3.3 8 1.216 350 333 100/LS2 110 3.3 7 1.258 333 333 101/LS1 3.85 8 1.125 345 286 101/LS2 3.65 8 380 301 Optical density measurements were carried out on the longitudinally stretched extrudates and the results are given in Table 24. The expected OD is obtained by substituting the expected thickness into the expression derived in COMPARATIVE EXAMPLE 5,

TABLE 24 Thickness [μm] OD Expected OD Example nr. measured expected TR924 OD ΔOD ΔOD/OD [X-rite]  91/LS1 320 286 1.00 0.81 0.19 0.19 0.76  92/LS1 325 286 1.05 0.81 0.24 0.23 0.82  92/LS2 323 301 1.00 0.83 0.17 0.17 0.78  93/LS1 318 286 1.06 0.81 0.25 0.23 0.85  94/LS1 350 333 1.21 0.87 0.34 0.28 0.98  94/LS2 330 333 1.02 0.87 0.15 0.15 0.80  95/LS1 365 333 0.87  96/LS1 300 290  96/LS2 335 305  96/LS3 350 319  97/LS1 360 333 1.17 0.87 0.30 0.26 0.97  98/LS1 330 333 1.08 0.87 0.21 0.19 0.90  99/LS1 330 286 1.13 0.81 0.32 0.28 0.92 100/LS1 350 333 1.18 0.87 0.31 0.26 1.00 100/LS2 333 333 1.10 0.87 0.23 0.21 0.89 101/LS1 345 286 1.20 0.81 0.39 0.32 1.02 101/LS2 380 301 1.23 0.83 0.40 0.32 1.00

Longitudinal stretching was accompanied by a decrease in density due to void-forming, this decrease in density clearly increasing as the proportion of PET04 increased i.e. surprisingly indicates that an increase in the isophthalic acid unit concentration in the aromatic polyester favours increased void-forming in the film. The increase in optical density due to void forming was in the range of 15 to 32%.

Transversal stretching was then performed on the longitudinally stretched films with a stretch time of 30 s and stretching speed of 1000%/min under the conditions given in Table 25. The density, measured thickness, the expected thickness, i.e. thickness if no void-forming on the basis of the extrudate thickness and the longitudinal and transversal stretch ratios, the measured optical density with the MacBeth TR924 densitometer in transmission mode with a visible filter, the expected optical density, i.e. the optical density calculated using the relationship disclosed in COMPARATIVE EXAMPLE 5 using the theoretical layer thickness values, and the difference between the observed optical density and the optical density expected due to a 2% by weight concentration of the particular titanium dioxide pigment used, ΔOD, are also given in Table 25.

TABLE 25 Transversal stretch temperature Density Thickness [μm] OD Expected ΔOD/ Example nr. ratio [° C.] [g/mL] Measured Expected TR924 OD ΔOD OD 91/LS1/BS1 3.3 135 1.284 101 87 1.00 0.35 0.65 0.65 92/LS1/BS1 3.3 134 1.219  95 87 1.01 0.35 0.66 0.65 92/LS2/BS1 3.3 135 102 91 0.99 0.37 0.62 0.63 93/LS1/BS1 3.3 132 100 87 1.04 0.35 0.69 0.66 93/LS1/BS2 1.234  97 87 (1.04) (0.35) (0.69) 0.66 94/LS1/BS1 3.5 100 1.074 140 95 1.20 0.39 0.81 0.67 94/LS1/BS2 3.5 96 1.002 135 95 1.25 0.39 0.86 0.69 94/LS2/BS1 3.5 96 1.158 116 95 1.10 0.39 0.71 0.64 95/LS1/BS1 3.3 132 1.228 140 101 1.10 0.41 0.69 0.63 96/LS1/BS1 3.3 122 110 88 1.06 0.36 0.70 0.66 96/LS2/BS1 3.3 122 135 93 1.18 0.38 0.80 0.68 96/LS3/BS1 3.3 122 150 97 1.11 0.40 0.71 0.64 97/LS1/BS1 3.5 95 1.071 145 95 1.21 0.39 0.82 0.68 98/LS1/BS1 3.5 96 1.070 138 95 1.20 0.39 0.81 0.67 99/LS1/BS1 3.3 134 1.195 105 87 1.10 0.35 0.75 0.68 100/LS1/BS1  3.5 95 1.055 147 95 1.20 0.39 0.81 0.67 100/LS2/BS1  3.5 95 1.140 112 95 1.05 0.39 0.66 0.63 101/LS1/BS1  3.3 135 0.990 169 87 1.32 0.35 0.97 0.73 101/LS2/BS1  3.3 135 185, 156 91 1.26 0.37 0.89 0.71 Transversal stretching reduced the density of the films still further with again the density decrease being greater as the proportion of PET04 increased. This again surprisingly indicates that an increase in the isophthalic acid unit concentration in the aromatic polyester favoured increased void-forming in the film. The decrease in density is smaller than would be expect simply based on the measured thicknesses compared with the expected thicknesses for non-voided films.

The results of Table 25 show that at approximately the same stretching temperature the contribution to the optical density of biaxially stretched films clearly increases to over 70% as the concentration of PET04 in the composition increases i.e. the concentration of isophthalic acid units in the polyester increases to the concentration of 10 mole % of the aromatic dicarboxylic acid in PET04 itself.

The presence of void-forming was demonstrated for several of the biaxially stretched films by clamping the films in an Instron 4411 apparatus and observing the changes in film thickness and optical density upon contacting the films with a soldering iron for 5 s at 150° C. The results of these experiments are given in Table 26.

TABLE 26 after heating at OD Thickness 150° C. for 5 s at (TR924) before pressure of 0.5 N/mm² % Change in before heating OD Thickness decrease thickness at Example nr. heating [μm] (TR924) [μm] in OD 150° C. [μm] 91/LS1/BS1 1.03 103 0.62 94 40 9 93/LS1/BS2 1.05 97 0.58 87 45 10 99/LS1/BS1 1.14 106 0.53 84 53 22 101/LS1/BS1  1.34 168 0.83 110 38 58 101/LS2/BS1  1.25 156 0.65 112 48 44 The results of Table 25 show that at approximately the same stretching temperature the contribution to the optical density of biaxially stretched films clearly increases as the concentration of PET04 in the composition increases i.e. the concentration of isophthalic acid units in the polyester increases to the concentration of 10 mole % of the aromatic dicarboxylic acid in PET04 itself.

INVENTION EXAMPLES 102 to 106

The ca. 1100 μm thick extrudates of INVENTION EXAMPLES 102 to 106 all with 2% by weight of titanium dioxide were produced as described for EXAMPLES 1 to 58 with 15% by weight of SAN or 15% by weight of ABS (MAGNUM 8391) and different weight ratios of T04 and PET04 as summarized in Table 27.

TABLE 27 Invention UVITEX TiO₂ Example PET02 PET04 MAGNUM SAN 06 OB- [wt nr. [wt %] [wt %] 8391 [wt %] [wt %] one [ppm] %] 102 83 0 15 — — 2.0 103 41.2 41.8 — 15 100 2.0 104 32.3 50.7 — 15 100 2.0 105 32 51 — 15 100 2.0 106 — 83 — 15 100 2.0 Stretching in the length direction was carried out for each extrudate as described in EXAMPLES 1 to 58 under the conditions given in Table 28. The expected thickness is the thickness based on the extrudate thickness and longitudinal as observed for non-voided films.

TABLE 28 Invention Longitudinal stretching Example force temperature Thickness [μm] OD OD nr. ratio [N/mm²] [° C.] Measured Expected TR924 [X-rite] 102/LS1 3.6 8 — 318 0.84 0.60 103/LS1* 3.3 7.97 375 333 1.08 0.96 103/LS2* 3.3 7.14 333 0.948 0.86 103/LS3* 3.3 9.67 333 1.19 1.09 104/LS1 3.8 8.3 120 300 290 0.94 104/LS2 3.6 8.23 96 330 305 0.96 104/LS3 3.3 8.6 90 365 333 104/LS4 3.1 8.2 80 380 355 105/LS1 3.6 8.23 114 330 1.26 0.96 106/LS1 3.85 8 — 320 1.24 1.00 *stretching speed 4.0 m/min Transversal stretching was then performed on the length-stretched films with a stretch time of 30 s and stretching speed of 1000%/min as described in EXAMPLES 59 to 78 under the conditions given in Table 29. The measured thickness, the expected thickness, i.e. thickness if no void-forming on the basis of the extrudate thickness and the longitudinal and transversal stretch ratios, the measured optical density with the MacBeth TR924 densitometer in transmission mode with a visible filter, the expected optical density, i.e. the optical density calculated using the relationship disclosed in COMPARATIVE EXAMPLE 5 using the theoretical layer thickness values, and the difference between the observed optical density and the optical density expected due to a 2% by weight concentration of the particular titanium dioxide pigment used, ΔOD, are also given in Table 29.

TABLE 29 Transversal stretch Invention temperature Density Thickness [μm] OD Expected Example nr. ratio [° C.] [g/mL] measured expected TR924 OD ΔOD 102/LS1/BS1 3.3 112 65, 85 0.73 103/LS1/BS1 3.5 115 1.19 140 95 0.925 0.39 0.535 103/LS1/BS2 3.5 100 1.08 116 95 1.05 0.39 0.66 103/LS2/BS1 3.5 100 1.17 123 95 1.01 0.39 0.62 104/LS1/BS1 3.3 114 110 88 1.01 0.36 0.65 104/LS2/BS1 3.3 113 135 93 1.17 0.38 0.69 104/LS3/BS1* 3.5 111 1.132 140 95 1.20 0.39 0.81 104/LS4/BS1 3.3 110 165 108 1.18 0.44 0.74 105/LS1/BS1 3.3 110 101 1.10 106/LS1/BS1 3.3 110 1.121 1.20 0.35 0.85 *stretching speed of 2000%/min

The elasticity (Young's) modulus and yield stress of the biaxially stretched extrudates were measured for INVENTION EXAMPLES 103/LS1/BS1, 103/LS1/BS2 and 103/LS2/BS1 and the results are summarized in Table 30 below:

TABLE 30 Elasticity modulus [N/mm²] Yield stress [N/mm²] longitudinal transversal longitudinal transversal direction direction direction direction 103/LS1/BS1 2908 4470 65.7 121 103/LS1/BS2 2594 3742 56.3 103.4 103/LS2/BS1 2965 4410 62.2 125.9

The presence of void-forming was demonstrated for the biaxially stretched film of INVENTION EXAMPLE 102/LS1/BS1 by clamping the film in an Instron 4411 apparatus and observing the change in film thickness and optical density upon contacting the film with a soldering iron for 5 s at 150° C. The results of these experiments are given in Table 31.

TABLE 31 after heating at OD Thickness 150° C. for 5 s at Change in (TR924) before pressure of 0.5 N/mm² % thickness Invention before heating OD thickness decrease at 150° C. Example nr. heating [μm] (TR924) [μm] in OD [μm] 102/LS1/BS1 0.73 85 0.54 79 26 6 The results of Table 31 show that at approximately the same stretching temperature the contribution to the optical density of biaxially stretched films clearly increases as the concentration of PET04 in the composition increases i.e. the concentration of isophthalic acid units in the polyester increases to the concentration of 10 mole % of the aromatic dicarboxylic acid in PET04 itself.

The presence of void-forming was also demonstrated for the biaxially stretched films of INVENTION EXAMPLES 99/LS1/BS1 and 100/LS1/BS1 by clamping the films in an Instron 4411 apparatus and observing the changes in film thickness and optical density upon contacting the film with a soldering iron for 5 s at various temperatures. The results of these experiments are given in Tables 32 and 33.

TABLE 32 OD OD (TR924) after heating for 5 s ΔOD % Invention before at a pressure of 0.5 N/mm² at at decrease Example nr heating 122° C. 130° C. 150° C. 170° C. 190° C. 150° C. in OD 105/LS1/BS1 1.10 0.84 0.83 0.68 0.62 0.57 0.42 38 106/LS1/BS1 1.19 0.86 0.78 0.60 0.50 — 0.60 50

TABLE 33 Film thick- ness before Film thickness [μm] after heating for 5 s Invention heating at a pressure of 0.5 N/mm² at Example nr [μm] 122° C. 130° C. 150° C. 170° C. 190° C. 105/LS1/BS1 125 117 117 113 106 84 106/LS1/BS1 100 94 88 81 73 — Reductions in optical density at 150° C. of 0.19, 0.42 and 0.60 were observed for the films of INVENTION EXAMPLE 102/LS1/BS1, 105/LS1/BS1 and 106/LS1/BS1 respectively corresponding to 26, 38 and 50%.

INVENTION EXAMPLES 107 to 109

The ca. 1100 μm thick extrudates of INVENTION EXAMPLES 107 to 109 all with 2% by weight of titanium dioxide and 15% by weight of SAN 06 were produced as described for EXAMPLES 1 to 58 with different weight ratios of TO4 and PET04 as summarized in Table 34.

TABLE 34 UVITEX Invention PET 02 PET 04 SAN 06 OB- TiO₂ Example nr. [% by wt] [% by wt] [% by wt] one [ppm] [% by wt] 107 32.3 50.7 15 100 2.0 108 — 83 15 100 2.0 109 — 83 15 100 2.0 Stretching in the length direction was carried out for each extrudate as described in EXAMPLES 1 to 58 under the conditions given in Table 35. The expected thickness is the thickness based on the extrudate thickness and longitudinal as observed for non-voided films.

TABLE 35 Invention Longitudinal stretching Example force temperature Thickness [μm] OD OD nr. ratio [N/mm²] [° C.] measured expected TR924 [X-rite] 107/LS1 3.3 8.6 90 365 333 107/LS2 3.1 8.2 80 380 355 108/LS1 3.85 8 — 320 1.24 1.00 109/LS1 3.62 8 — 323 1.09 0.82 Transversal stretching was then performed on the length-stretched films with a stretch time of 30 s and stretching speed of 1000%/min as described in EXAMPLES 59 to 78 under the conditions given in Table 36. The measured thickness, the expected thickness, i.e. thickness if no void-forming on the basis of the extrudate thickness and the longitudinal and transversal stretch ratios, the measured optical density with the MacBeth TR924 densitometer in transmission mode with a visible filter, the expected optical density, i.e. the optical density calculated using the relationship disclosed in COMPARATIVE EXAMPLE 5 using the theoretical layer thickness values, and the difference between the observed optical density and the optical density expected due to a 2% by weight concentration of the particular titanium dioxide pigment used, ΔOD, are also given in Table 36.

TABLE 36 Transversal stretching Invention temperature Density Thickness [μm] OD Expected Example nr. ratio [° C.] [g/mL] measured expected TR924 OD 107/LS1/BS1 3.3 153 107/LS2/BS1 — 150 162 108 0.44 108/LS1/BS1 — 160 101 0.99 109/LS1/BS1 — 160 116 0.98 The results of Table 36 show that at approximately the same stretching temperature the contribution to the optical density of biaxially stretched films clearly increases as the concentration of PET04 in the composition increases i.e. the concentration of isophthalic acid units in the polyester increases to the concentration of 10 mole % of the aromatic dicarboxylic acid in PET04 itself.

INVENTION EXAMPLE 110

The 1100 μm thick extrudate of INVENTION EXAMPLE 110 having a composition of 2% by weight of titanium dioxide, 100 ppm of UVITEX OB-one [ppm], 15% by weight of SAN 06 and 83% by weight of PET04 was produced as described for EXAMPLES 1 to 58. Stretching in the length direction was carried out for the extrudate as described in EXAMPLES 1 to 58 under four different sets of conditions as given in Table 37. The expected thickness is the thickness based on the extrudate thickness and longitudinal as observed for non-voided films.

TABLE 37 Invention Longitudinal stretch Thickness Example force temperature measured expected OD OD nr. ratio [N/mm²] [° C.] [μm] [μm] TR924 [X-rite] 110/LS1 3.8 8.3 120 300 290 0.94 110/LS2 3.6 8.23 96 330 305 0.96 110/LS3 3.3 8.6 90 365 333 110/LS4 3.1 8.2 80 380 355 Transversal stretching was then performed on the length-stretched films as described in EXAMPLES 59 to 78 under the conditions given in Table 38. The density, measured thickness and the expected thickness, i.e. thickness if no void-forming on the basis of the extrudate thickness and the longitudinal and transversal stretch ratios, are also given in Table 38.

TABLE 38 Transversal stretch Thickness Invention temperature time speed Density measured expected Example nr. ratio [° C.] [s] [%/min] [g/mL] [μm] μm] 110/LS3/BS1 3.3 86 30 1000 0.984 199 101 110/LS3/BS2 3.3 91 30 1000 0.978 185 101 110/LS3/BS3 3.3 98 30 1000 0.993 180, 190 101 110/LS3/BS4 3.3 100 30 1000 1.117 165 101 110/LS3/BS5 3.3 100 30 1000 150 101 110/LS3/BS6 101 30 1000 105 101 110/LS3/BS7 102 30 1000 135 101 110/LS2/BS1 3.3 106 30 1000 135 93 110/LS3/BS8 3.3 110 30 1000 150 101 110/LS4/BS1 3.3 110 30 1000 165 108 110/LS2/BS2 3.3 113 30 1000 135 93 110/LS1/BS1 3.3 114 30 1000 110 88 110/LS3/BS9 3.3 121 30 1000 1.199 150 101 110/LS2/BS3 3.3 123 30 1000 120 93 110/LS3/BS10 3.3 128 30 1000 1.221 140 101 110/LS3/BS11 3.3 132 30 1000 1.228 140 101 110/LS3/BS12 3.3 142 30 1000 1.242 140 101 110/LS4/BS2 150 162 108 110/LS3/BS13 3.3 153 30 1000 1.235 140 101 110/LS3/BS14 3.5 111 30 2000 1.132 140 95 110/LS3/BS15 110 10 1000 152 101

Biaxial stretching reduced the density of the films with the density decrease being greater the lower the transversal stretching temperature. However, the decrease in density is smaller than would be expect simply based on the measured thicknesses compared with the expected thicknesses based on the extrudate thickness, longitudinal stretch ratio and transversal stretch ratio as observed for non-voided films. This can be partly explained by the combination of two effects: the decrease in the density due to void forming on the one hand being to a degree compensated by the increase in the crystallinity of the polyester matrix due to biaxial stretching on the other.

Table 39 gives the measured thickness, the expected thickness, i.e. thickness if no void-forming on the basis of the extrudate thickness and the longitudinal and transversal stretch ratios, the optical density measured with a MacBeth TR924 densitometer in transmission mode with a visible filter, the expected optical density, i.e. the optical density calculated using the relationship disclosed in COMPARATIVE EXAMPLE 5 using the theoretical layer thickness values, and the difference between the observed optical density and the optical density expected due to a 2% by weight concentration of the particular titanium dioxide pigment used, ΔOD, together with the temperature at which the transversal stretching was carried out.

TABLE 39 Invention Stretch Thickness [μm] OD Expected OD Example nr. temperature [° C.] measured expected (TR924) OD ΔOD (X-rite) 110/LS3/BS1 86 199 101 1.35 0.41 0.95 0.110 110/LS3/BS2 91 185 101 1.32 0.41 0.91 0.107 110/LS3/BS3 98 180, 190 101 1.28; 1.36 0.41 0.87; 0.103 0.95 110/LS3/BS4 100 165 101 1.20 0.41 0.79 0.96 110/LS3/BS5 100 150 101 1.22 0.41 0.81 0.100 110/LS3/BS6 101 105 101 1.15 0.41 0.75 0.90 110/LS3/BS7 102 135 101 1.08 0.41 0.67 0.81 110/LS2/BS1 106 135 93 0.38 0.1005 110/LS3/BS8 110 150 101 0.41 0.94 110/LS4/BS1 110 165 108 1.18 0.44 0.74 0.91 110/LS2/BS2 113 135 93 1.17 0.38 0.79 0.905 110/LS1/BS1 114 110 88 1.01 0.36 0.65 0.805 110/LS3/BS9 121 150 101 1.14 0.41 0.73 0.89 110/LS2/BS3 123 120 93 0.38 0.88 110/LS3/BS10 128 140 101 1.10 0.41 0.69 0.86 110/LS3/BS11 132 140 101 1.10 0.41 0.69 0.85 110/LS3/BS12 142 140 101 1.10 0.41 0.69 0.83 110/LS4/BS2 150 162 108 0.44 0.85 110/LS3/BS13 153 140 101 1.10 0.41 0.69 0.86 It is clear from the results in Table 39, that the degree of void-forming, as indicated by the optical density not attributable to the 2% by weight of titanium dioxide present, increased with decreasing transversal stretch temperature regardless of the other conditions pertaining during the transversal stretch process.

Table 40 summarizes the stretch conditions, the thickness, expected thickness, optical density, expected optical density and non-attibutable increase in optical density as a result of void-forming for different films obtained at a stretch temperature of approximately 110° C.

The data in Table 40 shows that reducing the stretching time from 30 s to 10 s and increasing the stretching speed from 1000%/min to 2000%/min also promote void-forming.

TABLE 40 Transversal stretch OD Invention temperature time speed Thickness [μm] OD Expected (X- Example nr. [° C.] [s] [%/min] Measured Expected TR924 OD ΔOD rite) 110/LS3/BS14 111 30 2000 140 95 1.20 0.39 0.81 0.95 110/LS3/BS8 110 30 1000 150 101 0.41 0.94 110/LS4/BS1 110 30 1000 165 108 1.18 0.44 0.74 0.91 110/LS3/BS15 110 10 1000 152 101 1.22 0.41 0.81 1.00

The presence of void-forming was demonstrated for the biaxially stretched film of INVENTION EXAMPLE 110/LS3/BS1 by clamping the film in an Instron 4411 apparatus and observing the changes in film thickness and optical density upon contacting the film with a soldering iron for 5 s at various temperatures. The results of these experiments are given in Tables 41 and 42.

TABLE 41 OD (TR924) after heating for 5 s ΔOD % Invention OD before at a pressure of 0.5 N/mm² at at decrease Example nr heating 122° C. 130° C. 150° C. 170° C. 190° C. 150° C. in OD 110/LS3/BS1 1.36 1.18 1.12 1.02 0.82 0.72 0.42 25

TABLE 42 Film Film thickness [μm] after Invention thickness heating for 5 s at a Example before pressure of 0.5 N/mm² at nr heating [μm] 122° C. 130° C. 150° C. 170° C. 190° C. 110/LS3/ 199 163 157 147 139 145 BS1 A reduction in optical density at 150° C. of 0.42 was observed for the film of INVENTION EXAMPLE 110/LS1/BS1 corresponding to 25% accompanied by a reduction of 26% in layer thickness.

INVENTION EXAMPLES 111 to 113

The ca. 1100 μm thick extrudates of INVENTION EXAMPLES 111 to 113 of unpigmented dispersions of SAN 06 in aromatic polyester were produced as described for EXAMPLES 1 to 58 with different concentrations of SAN 06, TO4 and PET04 as summarized in Table 43.

TABLE 43 Invention Magnesium UVITEX Example PET02 PET04 SAN 06 acetate OB- nr. [% by wt] [% by wt] [% by wt] [ppm] one [ppm] 111 57.7 25.3 17 — 100 112 25.3 57.7 17 — 100 113 — 85.0 15 33 — Stretching in the length direction was carried out for each extrudate as described in EXAMPLES 1 to 58 under the conditions given in Table 44. The expected thickness is the thickness based on the extrudate thickness and longitudinal as observed for non-voided films.

TABLE 44 Invention Longitudinal stretch Thickness OD example force temperature Measured Expected OD Expected ΔOD/ [X- nr ratio [N/mm²] [° C.] [μm] [μm] TR924 OD ΔOD OD rite] 111/LS1 3.8 8.21 175 301 289 0.80 0.05 0.75 0.94 0.47 111/LS2 3.6 8.65 142 320 305 0.72 0.05 0.67 0.93 0.47 112/LS1 3.8 8.44 116 298 289 0.97 0.05 0.92 0.95 0.77 112/LS2 3.6 8.65 97 330 305 1.06 0.05 1.01 0.95 0.85 112/LS3 3.35 6.36 119 320 328 0.78 0.05 0.73 0.93 0.60 113/LS1 3.3 8.0 89 1.00 0.05 0.95 0.95 113/LS2 3.3 9.5 80 1.14 0.05 1.09 0.96 Transversal stretching was then performed on the length-stretched films with a stretch time of 30 s and stretching speed of 1000%/min as described in EXAMPLES 59 to 78 under the conditions given in Table 45. The measured thickness, the expected thickness, i.e. thickness if no void-forming on the basis of the extrudate thickness and the longitudinal and transversal stretch ratios, the measured optical density with the MacBeth TR924 densitometer in transmission mode with a visible filter, the expected optical density, i.e. 0.05 the optical density of polyethylene terephthalate almost completely determined by refraction effects at the two sides of the film, and the difference between the observed optical density and the optical density expected due to the aromatic polyester, ΔOD, are also given in Table 45.

TABLE 45 Transverse stretch Invention temperature Thickness [μm] OD Expected ΔOD/ example nr. ratio [° C.] Measured Expected TR924 OD ΔOD OD 111/LS2/BS1 3.3 124 82 92 0.83 0.05 0.78 0.94 112/LS1/BS1 3.3 120 97 88 0.99 0.05 0.94 0.95 112/LS2/BS1 3.3 120 123 92 1.04 0.05 0.99 0.95 113/LS1/BS1 3.5 90 165 95 1.08 0.05 1.03 0.95 113/LS1/BS2 3.5 88 175 95 1.10 0.05 1.05 0.95 113/LS1/BS3 3.5 85 172 95 1.15 0.05 1.10 0.96 113/LS1/BS4 3.5 82 195 95 1.20 0.05 1.15 0.96 113/LS2/BS1 3.5 94 227 95 1.22 0.05 1.17 0.96 113/LS2/BS2 3.5 85 228 95 1.30 0.05 1.25 0.96 113/LS2/BS3 3.5 81 227 95 1.30 0.05 1.25 0.96 113/LS2/BS4 3.5 77 235 95 1.34 0.05 1.29 0.96 113/LS2/BS5 3.5 75 232 95 1.33 0.05 1.28 0.96 The results in Table 45 show strongly increased opacification optical densities of 1.28 and 1.29 due to void-forming for the films of INVENTION EXAMPLES 113/LS2/BS4 and 113/LS2/BS5 with a linear polyester matrix with 10 mole % isophthalate compared with an opacification optical density of 0.78 due to void forming for the film of INVENTION EXAMPLE 111/LS2/BS1 with a linear polyester matrix with 3 mole % isophthalate.

The presence of void-forming was demonstrated for the biaxially stretched films of INVENTION EXAMPLES 111/LS2/BS1, 112/LS1/BS1 and 112/LS2/BS1 and the INVENTION EXAMPLE 113 series by clamping the films in an Instron 4411 apparatus and observing the changes in film thickness and optical density upon contacting the film with a soldering iron for 5 s at various temperatures. The results of these experiments are given in Tables 46 and 47.

TABLE 46 OD (TR924) after heating for OD 5 s at a pressure ΔOD % Invention before of 0.5 N/mm² at at decrease Example nr heating 122° C. 130° C. 150° C. 170° C. 190° C. 170° C. in OD 111/LS2/BS1 0.83 0.45 0.38 0.19 0.16 0.18 0.67 81 112/LS1/BS1 0.99 0.49 0.42 0.22 0.14 0.13 0.85 86 112/LS2/BS1 1.04 0.67 0.44 0.22 0.16 0.13 0.88 85 113/LS1/BS1 1.10 — — — 0.23 0.17 0.87 79 1.08 0.17 0.14 0.91 84 113/LS1/BS2 1.11 — — — 0.18 0.17 0.93 84 113/LS1/BS3 1.12 — — — 0.25 0.19 0.87 78 113/LS1/BS4 1.10 — — — 0.23 0.22 0.87 79 113/LS2/BS1 1.29 — — — 0.30 0.19 0.99 77 113/LS2/BS2 1.32 — — — 0.32 0.16 1.00 76 1.12 0.17 0.20 0.92 82 113/LS2/BS3 1.33 — — — 0.32 0.22 1.01 76 113/LS2/BS4 1.32 — — — 0.48 0.16 0.84 64 113/LS2/BS5 1.32 — — — 0.35 — 0.97 72

TABLE 47 Film Film thickness [μm] after Δ % thickness heating for 5 s at a pressure thickness decrease Invention before of 0.5 N/mm² at at in Example nr heating [μm] 122° C. 130° C. 150° C. 170° C. 190° C. 170° C. thickness 111/LS2/BS1 82 83 80 74 71 76 11 13 112/LS1/BS1 97 97 91 87 81 67 16 16 112/LS2/BS1 123 118 114 105 99 74 24 19 113/LS1/BS1 164 — — — 118 118 46 28 163 122 98 41 25 113/LS1/BS2 170 — — — 121 91 49 29 113/LS1/BS3 158 — — — 119 101 39 25 113/LS1/BS4 194 — — — 140 140 54 28 113/LS2/BS1 209 — — — 142 135 67 32 113/LS2/BS2 220 — — — 141 104 79 36 113/LS2/BS3 216 — — — 138 111 78 36 113/LS2/BS4 219 — — — 148 92 71 32 113/LS2/BS5 216 — — — 139 — 77 36 A reduction in optical density at 190° C. of 0.67, 0.85 and 0.88 was observed for the films of INVENTION EXAMPLES 111/LS2/BS1, 112/LS1/BS1 and 112/LS2/BS1 respectively corresponding to 81, 86 and 85%. In the INVENTION 113 series the reduction in optical density at 190° C. varied between 0.84 and 1.01 corresponding to 64 to 84%. These reductions in optical density were accompanied by a reduction of 13, 16 and 19% in layer thickness with 25 to 36% reduction in thickness being observed for the INVENTION EXAMPLE 113 series. These results show an extremely large reduction in optical density of up to 1.01 upon transparentizing polyester layers with 15 or 17 wt % SAN 06.

EXAMPLES 114 to 120

The ca. 1100 μm thick extrudates of INVENTION EXAMPLES 114 to 120 with 2% by weight of titanium dioxide and 15% by weight of SAN 06 were produced as described for EXAMPLES 1 to 58 with different concentrations of PET02 and PET06 as summarized in Table 32.

TABLE 48 Invention PET06 SAN 06 UVITEX Example NP* PET02 [% by [% by OB-one TiO₂ nr. [mol %] [% by wt] wt] wt] [ppm] [wt %] 114 5.2 66.3 16.7 15 100 2.0 115 8.5 55.7 27.3 15 100 2.0 116 12.6 43.0 40.0 15 100 2.0 117 15.8 33.3 49.7 15 — 2.0 118 17.0 29.7 53.3 15 100 2.0 119 21.5 16.3 66.7 15 — 2.0 120 26.7 1.0 82.0 15 — 2.0 *NP = neopentylene monomer units in polyester Stretching in the length direction was carried out for each extrudate as described in EXAMPLES 1 to 58 under the conditions given in Table 49. The expected thickness is the thickness based on the extrudate thickness and longitudinal as observed for non-voided films.

TABLE 49 Longitudinal stretch Thickness OD Example force speed temperature Density measured expected OD Expected ΔOD/ [X- nr. ratio [N/mm²] [m/min] [° C.] [g/mL] [μm] [μM] TR924 OD ΔOD OD rite] 114/BS1 3.3 9.55 4.0 387 333 0.84 115/BS1 3.3 9.55 4.0 366 333 0.82 116/BS1 3.3 8.27 4.0 366 333 0.77 117/BS1 3.3 8.0 90 1.147 350 333 1.19 0.87 0.32 0.27 0.97 118/BS1 3.3 7.64 4.0 362 333 0.75 119/BS1 3.3 6.79 4.0 266 333 0.80 120/BS1 3.3 7.62 4.0 383 333 0.81 120/BS2 3.3 8.59 4.0 385 333 0.93 Transversal stretching was then performed on the length-stretched film with a stretch time of 30 s and stretching speed of 1000%/min under the conditions given in Table 50. The measured thickness, the expected thickness, i.e. thickness if no void-forming on the basis of the extrudate thickness and the longitudinal and transversal stretch ratios, the measured optical density with the MacBeth TR924 densitometer in transmission mode with a visible filter, the expected optical density and the difference between the observed optical density and the optical density expected due to the aromatic polyester, ΔOD, are also given in Table 50.

The results in Table 50 clearly show very substantial opacification, 69% of the optical density realized being due to void-forming with a matrix of a blend of PET and PETG rather than PET or a blend of PET with a polyester of terephthalic acid, isophthalic acid and ethylene glycol such as PET03, PET04 and PET05.

TABLE 50 Stretch Expected OD Temperature Density Thickness thickness OD Expected ΔOD/ [X- Example nr. ratio [° C.] [g/mL] [μm] [μm] TR924 OD ΔOD OD rite] 114/LS1/BS1 3.5 100 1.17 141 95 0.81 115/LS1/BS1 3.5 95 1.07 123 95 0.82 116/LS1/BS1 3.5 95 1.12 136 95 0.81 117/LS1/BS1 3.5 95 0.944 150 95 1.28 0.89 0.39 0.69 1.02 118/LS1/BS1 3.5 95 1.12 133 95 0.85 119/LS1/BS1 3.5 100 1.03 135 95 0.87 120/LS1/BS1 3.5 100 0.96 139 95 0.83 120/LS2/BS1 3.5 100 147 95 0.98

The presence of void-forming was demonstrated for the biaxially stretched films of INVENTION EXAMPLES 114/LS1/BS1, 115/LS1/BS2, 116/LS1/BS1, 118/LS1/BS1 and 119/LS1/BS1 by clamping the films in an Instron 4411 apparatus and observing the changes in film thickness and optical density upon contacting the film with a soldering iron for 5 s at various temperatures. The results of these experiments are given in Table 51.

TABLE 51 Film after heating for 5 s at a pressure of 0.5 N/mm² thickness at 150° C. at 170° C. before OD film film thickness OD Invention heating before thickness measured Δ % Example nr [μm] heating [μm] OD [μm] [μm] % decrease measured Δ decrease 114/LS1/BS1 129 0.992 114 0.638 108.3 20.7 16.0 0.579 0.413 41.6 115/LS1/BS2 119 1.09 103 0.662 95.7 23.3 19.6 0.551 0.539 49.4 116/LS1/BS1 134 1.1 106 0.582 101.7 32.3 24.1 0.510 0.59 53.6 118/LS1/BS1 121 1.07 102 0.608 88.7 32.3 26.7 0.537 0.533 49.8 119/LS1/BS1 111 1.06 76 0.455 58 53 47.7 0.406 0.654 61.7 A reduction in optical density at 170° C. varying from 0.413 for the film of INVENTION EXAMPLE 114/LS1/BS1 to 0.654 for the film of INVENTION EXAMPLE 119/LS1/BS1 corresponding to 41.6 to 61.7%. These reductions in optical density were accompanied by a reduction of 16 to 47.7% in layer thickness. These results show a large reduction in optical density of up to 0.654 upon transparentizing polyester layers with 15 wt % SAN 06 and 2 wt % TiO₂.

EXAMPLE 121

The ca. 1100 μm thick extrudate of EXAMPLE 121 with 2% by weight of titanium dioxide, 15% by weight of TPX® DX820, poly(4-methyl-pentene), 33.3% by weight of PET02 and 49.7% by weight of PET04 was produced as described for EXAMPLES 1 to 58. Stretching in the length direction was carried out for each extrudate as described in EXAMPLES 1 to 58 under the conditions given in Table 52. The expected thickness is the thickness based on the extrudate thickness and longitudinal as observed for non-voided films.

TABLE 52 Longitudinal stretch Thickness OD Example Force Speed Density Measured Expected OD Expected ΔOD/ [X- nr. Ratio [N/mm²] [m/min] [g/mL] [μm] [μm] TR924 OD ΔOD OD rite] 121/BS1 3.3 5.21 4.0 1.147 333 1.10 0.87 0.23 0.21 0.96 Transversal stretching was then performed on the length-stretched film with a stretch time of 30 s and stretching speed of 1000%/min under the conditions given in Table 52. The measured thickness, the expected thickness, i.e. thickness if no void-forming on the basis of the extrudate thickness and the longitudinal and transversal stretch ratios, the measured optical density with the MacBeth TR924 densitometer in transmission mode with a visible filter, the expected optical density and the difference between the observed optical density and the optical density expected due to the aromatic polyester, ΔOD, are also given in Table 53.

TABLE 53 Transversal stretch Thickness Temperature Density Measured Expected OD Expected ΔOD/ Example nr. Ratio [° C.] [g/mL] [μm] [μm] TR924 OD ΔOD OD 121/LS1/BS1 3.5 100 0.64 1.08 0.39 0.69 0.64

The results in Table 53 clearly show very substantial opacification, 64% of the optical density realized being due to void-forming with a matrix of PET04 with TPX as crystalline dispersed phase with a particle size of ca. 10 μm. However, the elasticity (Young's) modulus in the longitudinal direction at 1258 N/mm² and the yield stress in the longitudinal direction at 26.4 N/mm² were substantially lower than for materials using SAN as opacity-producing agent, see results for INVENTION EXAMPLES 103/LS1/BS1, 103/LS1/BS2 and 103/LS2/BS1.

The present invention may include any feature or combination of features disclosed herein either implicitly or explicitly or any generalisation thereof irrespective of whether it relates to the presently claimed invention. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Having described in detail preferred embodiments of the current invention, it will now be apparent to those skilled in the art that numerous modifications can be made therein without departing from the scope of the invention as defined in the following claims.

All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations of those preferred embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. 

1. A permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film exclusive of foam.
 2. The pattern according to claim 1, wherein said film further comprises at least one inorganic opacifying pigment.
 3. The pattern according to claim 2, wherein said at least one inorganic opacifying pigment is selected from the group consisting of silica, zinc oxide, zinc sulphide, lithopone, barium sulphate, calcium carbonate, titanium dioxide, aluminium phosphates and clays.
 4. The pattern according to claim 1, wherein said film comprises ≦5% by weight of inorganic opacifying pigment each with a refractive index of less than 2.0.
 5. The pattern according to claim 1, wherein said film comprises a polymer as a continuous phase and dispersed uniformly therein an amorphous high polymer with a higher glass transition temperature than the glass transition temperature of said continuous phase and/or a crystalline high polymer with a melting point higher than said glass transition phase of said continuous phase and inorganic opacifying pigment as particles all having a refractive index of at least 2.0 in a total concentration of between 0.5 and 5% by weight of said film.
 6. The pattern according to claim 1, wherein said film is a biaxially stretched film.
 7. The pattern according to claim 1, wherein said film comprises a polyolefin as continuous phase.
 8. The pattern according to claim 7, wherein said polyolefin is polypropylene of poly(4-methylpentene).
 9. The pattern according to claim 1, wherein said film comprises a linear polyester as continuous phase.
 10. The pattern according to claim 9, wherein in said continuous phase linear polyester matrix is uniformly dispersed from 7 to 35% by weight of said film of a high polymer, said high polymer being an amorphous high polymer having a higher glass transition temperature than the glass transition temperature of said linear polyester and/or a crystalline high polymer having a higher melting point than the glass transition temperature of said linear polyester.
 11. The pattern according to claim 1, wherein said non-transparent microvoided axially stretched self-supporting polymeric film further comprises a whitening agent.
 12. The pattern according to claim 9, wherein said linear polyester has monomer components consisting essentially of at least one aromatic dicarboxylic acid and at least one aliphatic diol.
 13. The pattern according to claim 5, wherein said high polymer is at least partially crosslinked.
 14. The pattern according to claim 5, wherein said amorphous high polymer is at least one polymer selected from the group consisting of a polymethylmethacrylate, a SAN polymer, and a copolymer of acrylonitrile, butadiene and styrene.
 15. The pattern according to claim 4, wherein said inorganic opacifying pigment each with a refractive index of less than 2.0 is selected from the group consisting of zinc oxide, silica, barium sulphate, calcium carbonate, aluminium phosphates and clays.
 16. The pattern according to claim 3, wherein inorganic opacifying pigment as particles all having a refractive index of at least 2.0 in a total concentration of between 0.5 and 5% by weight of said film is selected from the group consisting of zinc oxide, zinc sulphide and titanium dioxide.
 17. The pattern according to claim 11, wherein said whitening agent is selected from the group consisting of bis-benzoxazoles; benzotriazole-phenylcoumarins; naphthotriazole-phenylcoumarins; triazine-phenylcoumarins and bis(styryl)biphenyls.
 18. The pattern according to claim 9, wherein said linear polyester has an inherent viscosity determined in a 0.5 g/dL solution of 60 wt % phenol and 40 wt % ortho-dichloro-benzene at 25° C. of 0.45 to 0.8 dl/g.
 19. The pattern according to claim 10, wherein said high amorphous polymer and/or said high crystalline polymer is present in said polyester matrix as particles with a diameter of less than 10 μm.
 20. The pattern according to claim 1, wherein said film is usable as a synthetic paper.
 21. The pattern according to claim 1, wherein said pattern is detectable by touch or differences in glossiness.
 22. The pattern according to claim 1, wherein said pattern is a watermark.
 23. A layer configuration comprising a permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film exclusive of foam.
 24. The layer configuration according to claim 23, wherein said film with a permanent transparent pattern is provided on at least one side with a transparent overprintable layer.
 25. The layer configuration according to claim 23, wherein said film with a permanent transparent pattern is provided on at least one side with a transparentizable overprintable layer.
 26. A security document comprising a permanent transparent pattern in a permanent transparent pattern in a non-transparent microvoided axially stretched self-supporting polymeric film exclusive of foam.
 27. The security document according to claim 26, wherein said security document is an identity card.
 28. A process for obtaining a permanent transparent pattern comprising the step of: image-wise application of heat optionally supplemented by the application of pressure to a non-transparent microvoided axially stretched self-supporting polymeric film exclusive of foam.
 29. The process according to claim 28, wherein said film further comprises ≦3% by weight of inorganic opacifying pigment each with a refractive index of less than 2.0.
 30. The process according to claim 28, wherein said film is biaxially stretched.
 31. The process according to claim 28, wherein said film comprises a polyolefin as continuous phase.
 32. The process according to claim 31, wherein said polyolefin is polypropylene.
 33. The process according to claim 28, wherein said film comprises a linear polyester as continuous phase.
 34. The process according to claim 33, wherein in said continuous phase linear polyester matrix is uniformly dispersed from 7 to 35% by weight of said film of a high polymer, said high polymer being an amorphous high polymer having a higher glass transition temperature than the glass transition temperature of said linear polyester and/or a crystalline high polymer having a higher melting point than the glass transition temperature of said linear polyester.
 35. The process according to claim 28, wherein said non-transparent microvoided axially stretched self-supporting polymeric film further comprises a whitening agent. 